Type of site
|Image/Video hosting service|
|Founded||Vancouver, British Columbia, Canada, 2004|
|Created by|| Stewart Butterfield |
|Parent|| Ludicorp (2004–2005)|
Yahoo! Inc. (2005–2017)
|Users||112 million |
|Launched||February 10, 2004 |
Flickr ( /ˈflɪkər/ FLI-kər; pronunciation (help·info)) is an American image hosting and video hosting service, as well as an online community, founded in Canada and headquartered in the United States. It was created by Ludicorp in 2004 and was a popular way for amateur and professional photographers to host high-resolution photos.   It has changed ownership several times and has been owned by SmugMug since April 20, 2018. 
As of June 10,2015, [update] Flickr had a total of 112 million registered members and more than 3.5 million new images uploaded daily.   On August 5, 2011, the site reported that it was hosting more than 6 billion images.  Photos and videos can be accessed from Flickr without the need to register an account, but an account must be made to upload content to the site. Registering an account also allows users to create a profile page containing photos and videos that the user has uploaded and also grants the ability to add another Flickr user as a contact. For mobile users, Flickr has official mobile apps for iOS,  Android,  and an optimized mobile site. 
Flickr was launched on February 10, 2004 by Ludicorp, a Vancouver-based company founded by Stewart Butterfield and Caterina Fake. The service emerged from tools originally created for Ludicorp's Game Neverending, a web-based massively multiplayer online game. Flickr proved a more feasible project, and ultimately Game Neverending was shelved,  Butterfield later launched a similar online game, Glitch, which was shut down on November 14, 2012.  
Early versions of Flickr focused on a chat room called FlickrLive, with real-time photo exchange capabilities.  The successive evolutions focused more on the uploading and filing back-end for individual users and the chat room was buried in the site map. It was eventually dropped as Flickr's back-end systems evolved away from Game Neverending's codebase.  Key features of Flickr not initially present are tags, marking photos as favorites, group photo pools and interestingness, for which a patent was granted. 
In addition to being a popular website for users to share and embed personal photographs and an online community, in 2004, the service was widely used by photo researchers and by bloggers to host images that they embed in blogs and social media. 
Yahoo! acquired Ludicorp and Flickr on March 20, 2005. The acquisition reportedly cost $22 million to $25 million.  During the week of June 26, 2005 to July 2, 2005, all content was migrated from servers in Canada to servers in the United States, and all resulting data became subject to United States federal law.  [ further explanation needed ] On May 3, 2007, Yahoo! announced that Yahoo! Photos would close down on September 20, 2007, after which all photos would be deleted; users were encouraged to migrate to Flickr.  On January 31, 2007, Flickr announced that "Old Skool" members (those who had joined before the Yahoo! acquisition) would be required to associate their account with a Yahoo! identity by March 15, 2007 to continue using the service.  This move was criticized by some users. 
Flickr upgraded its services from "beta" to "gamma" status on May 16, 2006, the changes attracted positive attention from Lifehacker.  On December 13, 2006, upload limits on free accounts were increased to 100 MB a month (from 20 MB) and were removed from Flickr Pro accounts, which originally had a 2 GB per month limit.  On April 9, 2008, Flickr began allowing paid subscribers to upload videos, limited to 90 seconds in length and 150 MB in size. On March 2, 2009, Flickr added the facility to upload and view HD videos, and began allowing free users to upload normal-resolution video. At the same time, the set limit for free accounts was lifted.  In 2009, Flickr announced a partnership with Getty Images in which selected users could submit photographs for stock photography usage and receive payment. On June 16, 2010, this was changed so that users could label images as suitable for stock use themselves. 
On May 20, 2013, Flickr launched the first stage of a major site redesign, introducing a "Justified View" close-spaced photo layout  browsed via "infinite scrolling" and adding new features, including one terabyte of free storage for all users, a scrolling home page (mainly of contacts photos and comments) and updated Android app.   The Justified View is paginated between 72 and 360 photos per page but unpaginated in search result presentation. Tech Radar described the new style Flickr as representing a "sea change" in its purpose.  Many users criticized the changes, and the site's help forum received thousands of negative comments.  On March 25, 2014, Flickr's New Photo Experience, a user interface redesign, left beta. 
On May 7, 2015, Yahoo! overhauled the site, adding a revamped Camera Roll, a new way to upload photos and upgraded the site's apps. The new Uploadr application was made available for Macs, Windows and mobile devices. 
In early May 2019, SmugMug announced the migration of Flickr data - 100+ million accounts and billions of photos and videos - from former owner Yahoo's servers to Amazon Web Services (AWS) in a planned 12-hour transition on May 22, 2019. 
On June 13, 2008, Flickr co-founder Stewart Butterfield announced his resignation on July 12, 2008, which followed that of his wife and co-founder Caterina Fake, who left the company on the same day.  Butterfield wrote a humorous resignation letter to Brad Garlinghouse. 
On December 14, 2008, The Guardian reported that three employees had been laid off as Yahoo! continued to reduce its workforce,  and on November 30, 2010, CNET reported Yahoo! was on the verge of a major layoff affecting 10% to 20% of its workforce. Flickr was specifically named as a target for these layoffs. 
On June 13, 2017, Verizon Communications acquired Yahoo!, including Flickr.   Verizon reorganized Yahoo!, along with AOL, into a new umbrella company, Oath, which was renamed as Verizon Media on January 8, 2019.
On April 20, 2018, SmugMug acquired Flickr from Verizon's Oath and put an end to Flickr 1 TB storage plan for free users, these users had until February 5, 2019 to convert to 'Pro' accounts or their photo streams would be reduced to a maximum of 1,000 pictures.   The deadline was later extended to March 12, 2019. The reasons cited were that the existing model was unsustainable by a medium-sized company which could not get revenues by selling profiles of the users. The sentiment was generally agreed on among the professionals.  This policy, however, was never implemented and was abandoned in March, 2022 in favor of a policy that restricted content unless the user upgraded and paid for a Pro account. 
Flickr has always offered two types of accounts: Free and Pro. Until January 7, 2019, free accounts had up to 1 TB of storage. On January 8, 2019, the account offerings changed.  The free option is limited to 1,000 photos or videos stored, with videos limited to 3 minutes. After January 8, 2019, members over the limit could no longer upload new photos to Flickr. On February 5, 2019, a free account's older content would be deleted automatically if it contains more than 1,000 photos and they do not subscribe to Pro,  with the exception of content that was already uploaded with a Creative Commons license before November 1, 2018. 
The Pro option features "unlimited" storage, advanced statistics, advertising-free browsing, videos up to 10 minutes in length, "premier" customer service, and promotional offers with other partners. 
In May 2011, Flickr added an option to easily reverse an account termination, motivated by the accidental deletion of a Flickr user's account, and public reporting of its protracted restoration.  Flickr may delete accounts without giving any reason or warning to the account's owner. 
As a result of the SmugMug buyout, Flickr added the ability for users to download all of their account data, such as photo albums, contacts, and comments. 
The images a photographer uploads to Flickr go into their sequential "photostream", the basis of a Flickr account. All photostreams can be displayed as a justified view, a slide show, a "detail" view or a datestamped archive. Clicking on a photostream image opens it in the interactive "photopage" alongside data, comments and facilities for embedding images on external sites.
Users may label their uploaded images with titles and descriptions, and images may be tagged, either by the uploader or by other users, if the uploader permits it. These text components enable computer searching of Flickr. Flickr was an early website to implement tag clouds, which were used until 2013, providing access to images tagged with the most popular keywords. Tagging was further revised in the photopage redesign of March 2014. Flickr has been cited as a prime example of effective use of folksonomy. 
Users can organize their Flickr photos into "albums" (formerly "sets") which are more flexible than the traditional folder-based method of organizing files, as one photo can belong to one album, many albums, or none at all. Flickr provides code to embed albums into blogs, websites and forums. Flickr albums represent a form of categorical metadata rather than a physical hierarchy. Geotagging can be applied to photos in albums,  and any albums with geotagging can be related to a map using imapflickr. The resulting map can be embedded in a website.  Flickr albums may be organized into "collections", which can themselves be further organized into higher-order collections.
Organizr is a Web application for organizing photos within a Flickr account that can be accessed through the Flickr interface. It allows users to modify tags, descriptions and set groupings, and to place photos on a world map (a feature provided in conjunction with Yahoo! Maps). It uses Ajax to emulate the look, feel and quick functionality of desktop-based photo-management applications, such as Google's Picasa and F-Spot. Users can select and apply changes to multiple photos at a time, as an alternative to the standard Flickr interface for editing.
Flickr provides both private and public image storage. A user uploading an image can set privacy controls that determine who can view the image. A photo can be flagged as either public or private.  Private images are visible by default only to the uploader, but they can also be marked as viewable by friends and/or family. Privacy settings also can be decided by adding photographs from a user's photostream to a "group pool". If a group is private all the members of that group can see the photo. If a group is public the photo becomes public as well. Flickr also provides a "contact list" which can be used to control image access for a specific set of users in a way similar to that of LiveJournal. In November 2006, Flickr created a "guest pass" system that allows private photos to be shared with non-Flickr members. This setting allows sets or all photos under a certain privacy category (friends or family) to be shared.  Many members allow their photos to be viewed by anyone, forming a large collaborative database of categorized photos. By default, other members can leave comments about any image they have permission to view and, in many cases, can add to the list of tags associated with an image.
The core functionality of the site relies on standard HTML and HTTP features, allowing for wide compatibility among platforms and browsers; Flickr's functionality includes RSS and Atom feeds and an API that enables independent programmers to expand its services. This includes a large number of third-party Greasemonkey scripts that enhance and extend the functionality of Flickr. In 2006, Flickr was the second most extended site on userscripts.org.  Organizr and most of Flickr's other text-editing and tagging interfaces use Ajax, with which most modern browsers are compliant. Images can be posted to the user's photostream via email attachments, which enables direct uploads from many cameraphones and applications. Flickr uses the Geo microformat on over 3 million geotagged images. 
According to the company, as of August 2009 [update] Flickr is hosted on 62 databases across 124 servers, with about 800,000 user accounts per pair of servers.  Based on information compiled by highscalability.com, as of November 2007 [update] the MySQL databases are hosted on servers that are Linux-based (from Red Hat), with a software platform that includes Apache, PHP (with PEAR and Smarty), shards, Memcached, Squid, Perl, ImageMagick and Java; the system administration tools include Ganglia, SystemImager, Subcon and CVSup. 
Signed-in Flickr users can "Follow" the Photostreams of other Flickr photographers. Reciprocating this process is optional. A user's homepage contains a stream of their Contacts' photos at 2/3 screensize. 
Groups are another major means of interaction with fellow members of Flickr around common photography interests. A Flickr Group can be started by any Flickr user, who becomes its administrator and can appoint moderators. Groups may either be open access or invitation-only, and most have an associated pool of photos. The administrator of the Flickr group can monitor and set restrictions for the group, assign awards to members, and may curate and organize the photo content. Recent uploads to a group will sometimes appear on its members' homepages. Group photo pools may be displayed in the "Justified View" or as a slideshow.
"Galleries" of photos from other photostreams may be curated by any signed-up Flickr user, provided the feature is not disabled by the photo's uploader, these are then publicly viewable. 
Any Flickr user can post comments to a Flickr photo on its photopage, unless this has been disabled by the uploader, and users can "favorite" a photo. A user's favorites can be viewed in a justified or slideshow display. 
Users of Windows Photo Gallery, Apple's iPhoto (version 8), Adobe's Lightroom 3.2, Apple's Aperture (version 3.0), darktable, and digiKam have the ability to upload their photos directly to Flickr. They can also automatically update their status on other social networking services when they upload their images to Flickr.  Flickr provides a desktop client for Mac OS X and Windows that allows users to upload photos without using the web interface. Uploadr allows drag-and-drop batch uploading of photos, the setting of tags and descriptions for each batch, and the editing of privacy settings. 
Flickr has entered into partnerships with many third parties. Flickr had a partnership with the Picnik online photo-editing application that included a reduced-feature version of Picnik built into Flickr as a default photo editor.  On April 5, 2012, Flickr replaced Picnik with Aviary as its default photo editor.  In addition to using commercial mapping data, Flickr now uses OpenStreetMap mapping for various cities; this began with Beijing during the run-up to the 2008 Olympic games. As of October 2008 [update] , this is used for Baghdad, Beijing, Kabul, Sydney and Tokyo.   OpenStreetMap data is collected by volunteers and is available under the Open Database License. Flickr offers printing of various forms of merchandise, including business cards, photo books, stationery, personalized credit cards and large-size prints from companies such as Moo, Blurb, Tiny Prints, Capital One, Imagekind, and QOOP. The Flickr partnership with Getty Images to sell stock photos from users is under review as of early 2014.  
In March 2007, Flickr added new content filtering controls that let members specify by default what types of images they generally upload (photo, art/illustration, or screenshot) and how "safe" (i.e., unlikely to offend others) their images are, as well as specify that information for specific images individually.  Individual images are assigned to one of three categories: "safe", "moderate" and "restricted".  Users can specify the same criteria when searching for images. There are some restrictions on searches for certain types of users: non-members must always use SafeSearch, which omits images noted as potentially offensive, while members whose Yahoo! accounts indicate that they are underage may use SafeSearch or moderate SafeSearch, but cannot turn SafeSearch off completely. The system achieves a fairly good separation of family-friendly photos and adult content; generic image searches normally produce no pornographic results, with the visibility of adult content restricted to users and dedicated Flickr communities who have opted into viewing it. 
Flickr has used this filtering system to change the level of accessibility to "unsafe" content for entire nations, including South Korea, Hong Kong and Germany. In summer 2007, German users staged a "revolt" over being assigned the user rights of a minor. See Censorship below.
Flickr offers users the ability to either release their images under certain common usage licenses or label them as "all rights reserved". The licensing options primarily include the Creative Commons 2.0 attribution-based and minor content-control licenses – although jurisdiction and version-specific licenses cannot be selected. As with "tags", the site allows easy searching of only those images that fall under a specific license. 
On January 16, 2008, Flickr launched a program called "The Commons on Flickr."  Several international cultural institutions share images using a "no known copyright restrictions" through the program. According to Flickr, the goal of the program is to "firstly show you hidden treasures in the world's public photography archives, and secondly to show how your input and knowledge can help make these collections even richer." Participants include the National Museum of Denmark, Powerhouse Museum, George Eastman Museum, Library of Congress, Nationaal Archief, National Archives and Records Administration, National Library of Scotland, State Library of New South Wales, and Smithsonian Institution.  
In May 2009, White House official photographer Pete Souza began using Flickr as a conduit for releasing White House photos. The photos were initially posted with a Creative Commons Attribution license requiring that the original photographers be credited. Flickr later created a new license which identified them as "United States Government Work", which does not carry any copyright restrictions. 
In March 2015, Flickr added the Creative Commons Public Domain Mark and Creative Commons Zero (CC0) to its licensing options.  The Public Domain Mark is meant for images that are no longer protected by copyright. CC0 is used for works that are still protected by copyright or neighbouring rights, but where the rightsholders choose to waive all those rights.
Flickr became an immediate success and is seen as a successful example of "Web 2.0", and a year later was purchased by Yahoo!.   Initially the site was most popular with professional photographers and graphic designers as well as bloggers who used it as an image repository. In 2007, Flickr was the 19th most popular website on the Internet according to its Alexa Rank.  However, since then, its popularity has declined relative to social media platforms with photo sharing capabilities (such as Facebook and Instagram), as well as cloud file storage services (such as Dropbox).  By 2021, Flickr's Alexa Rank declined significantly, yet indicated that the website was still among the top 500 most popular websites globally. 
On June 12, 2007, in the wake of the rollout of localized language versions of the site, Flickr implemented a user-side rating system for filtering out potentially controversial photos. Simultaneously, users with accounts registered with Yahoo! subsidiaries in Germany, Singapore, Hong Kong and Korea were prevented from viewing photos rated "moderate" or "restricted" on the three-part scale used. Many Flickr users, particularly in Germany, protested against the new restrictions, claiming unwanted censorship from Flickr and Yahoo. 
Flickr management, unwilling to go into legal details, implied that the reason for the stringent filtering was some unusually strict age-verification laws in Germany. The issue received attention in the German national media, especially in online publications. Initial reports indicated that Flickr's action was a sensible, if unattractive, precaution against prosecution,  although later coverage implied that Flickr's action may have been unnecessarily strict.  On June 20, 2007, Flickr reacted by granting German users access to "moderate" (but not "restricted") images, and hinted at a future solution for Germany, involving advanced age-verification procedures.
Since June 1, 2009, Flickr has been blocked in China in advance of the 20th anniversary of the Tiananmen Square protests of 1989. 
Michael Arrington of TechCrunch  and the Electronic Frontier Foundation  have criticised Flickr for its heavy-handed implementation of the Digital Millennium Copyright Act (DMCA) and Online Copyright Infringement Liability Limitation Act (OCILLA). Under OCILLA, a service provider such as Flickr is obliged to delete or disable access to content as soon as they receive an official notice of infringement, to maintain protection from liability.  After having one of his own pictures taken down following an incorrect DMCA claim, British comedian Dave Gorman researched the issue and concluded that if the Flickr user was not based in the United States or they were, but the person filing the notice of infringement was not, Flickr deleted the disputed content immediately. Even if the user could successfully demonstrate that the content did not infringe upon any copyright, Flickr did not, according to Gorman, replace the deleted content. He argued that this was contrary to its obligations in responding to a counter-notice.  Shortly afterward, Flickr changed its policy. 
In 2019, Flickr added new theft detection tool options to certain users. Some subscribers will be provided "copy-protection tools that can detect if their images have been used without permission," the BBC reported in 2019, noting "Flickr Pro subscribers will be able to monitor up to 1,000 images and send automated copyright claims to people or companies that use their photos." 
In November 2014, Flickr announced that it would sell wall-sized prints of photos from the service that are licensed under Creative Commons licenses allowing commercial use. Although its use of the photos in this manner is legal and allowed under the licenses, Flickr was criticized by users for what they perceived to be unfair exploitation of artists' works, as all the profits from these offerings go to Yahoo! and are not shared with their respective photographers, and users were not given a means of opting-out from the program without placing their photos under a more restrictive non-commercial license. By contrast, a similar opt-in program for "licensed" photos does give photographers a 51% share of sales. On December 19, 2014, Flickr General Manager Bernardo Hernandez announced they would pull all Creative Commons-licensed images from the program and issue refunds, stating that "Subsequently, we'll work closely with Creative Commons to come back with programs that align better with our community values."   
On November 1, 2018, Flickr announced new restrictions for its users. 
On March 17, 2022, Flickr revealed that it had not in fact deleted any photos for exceeding storage limits. However, it announced that it would soon implement a policy limiting the sharing of "moderate" or "restricted" content to Pro users, and limiting free users to 50 "non-public" images. Images beyond these limits would be at risk for deletion. 
Image sharing, or photo sharing, is the publishing or transfer of digital photos online. Image sharing websites offer services such as uploading, hosting, managing and sharing of photos. This function is provided through both websites and applications that facilitate the upload and display of images. The term can also be loosely applied to the use of online photo galleries that are set up and managed by individual users, including photoblogs. Sharing means that other users can view but not necessarily download images, and users can select different copyright options for their images.
Photobucket is an American image hosting and video hosting website, web services suite, and online community. Photobucket hosts more than 10 billion images from 100 million registered members. Photobucket's headquarters are in Denver, Colorado. The website was founded in 2003 by Alex Welch and Darren Crystal and received funding from Trinity Ventures. It was acquired by Fox Interactive Media in 2007. In December 2009, Fox's parent company, News Corp, sold Photobucket to Seattle mobile imaging startup Ontela. Ontela then renamed itself Photobucket Inc. and continues to operate as Photobucket.
Yahoo! Photos was a photo sharing service launched on March 28, 2000 and owned by Yahoo!, designed specifically for Yahoo! users. Users created individual photo albums, categorized their photos and placed them in the corresponding albums. Users were also able to set access of their albums by publishing them for the viewing pleasure of everyone, disabling access, or marking them as private folders for their own viewing.
The following tables compare general and technical information for a number of current, notable video hosting services. Please see the individual products' articles for further information.
ImageShack is a subscription-based image hosting website headquartered at Los Gatos, California.
Picasa Web Albums (PWA) was an image hosting and sharing web service from Google, often compared to Flickr and similar sites. The service links with Google's photo organizing desktop program Picasa. It was discontinued in May 2016 and succeeded by Google Photos which does not support sharing photo albums on the public world wide web.
Twango was an online media sharing site that supported multiple file types such as photos, video, audio, and documents. Founded in 2004 by Jim Laurel, Philip Carmichael, Randy Kerr, Serena Glover and Michael Laurel in Redmond, Washington, it provided users a means of repurposing their media, including sharing, editing, organizing and categorizing. In addition, Twango saved all the original media and its metadata. Non-members were free to browse the site, however only members could upload media to the site. Sign up for a basic account was free, and provided 250 megabytes of upload bandwidth a month.
Panoramio was a geo-located tagging, photo sharing mashup active between 2005 and 2016. Photos uploaded to the site were accessible as a layer in Google Earth and Google Maps. The site's goal was to allow Google Earth users to learn more about a given area by viewing the photos that other users had taken at that location. Panoramio was acquired by Google in 2007. In 2009 the website was among 1000 most popular websites worldwide.
Niconico (known before 2012 as Nico Nico Douga is a Japanese video-sharing service on the web. "Niconico" or "nikoniko" is the Japanese ideophone for smiling. As of 2021, Niconico is the 34th most-visited website in Japan, according to Alexa Internet.
Stage6 was a video sharing website owned and operated by DivX, Inc., where users could upload, share, and view video clips. Stage6 was different from other video services in that it streamed high quality video clips that were user-encoded with DivX and Xvid video codecs.
Ipernity is a non-commercial photo sharing community which is financed exclusively by membership dues without any intention of making a profit. By means of the Ipernity Members Association (IMA), the community operates its own website for the protected private exchange of digital content such as photos, videos, audio files and blogs, as well as for the worldwide publication of selected content.
Fotki is a digital photo sharing, video sharing and media social network website and web service suite; it is one of the world's largest social networking sites. Fotki licenses photo-sharing software for many global companies, such as Telecom Italia, Alice.it, Sears, Mark Travel, Vegas.com, Funjet.com etc.
Tumblr is a microblogging and social networking website founded by David Karp in 2007 and currently owned by American company Automattic. The service allows users to post multimedia and other content to a short-form blog. Users can follow other users' blogs. Bloggers can also make their blogs private. For bloggers, many of the website's features are accessed from a "dashboard" interface. As of March 2023, Tumblr hosts more than 572 million blogs.
Wikimedia Commons is a media repository of free-to-use images, sounds, videos and other media. It is a project of the Wikimedia Foundation.
Koinup is an image and video hosting service, web portal and online community for virtual world users. It is used both as a photo and video repository platform and as a tool to share virtual world screenshots, photographs and machinima. As of November 2008, it claims to host more than 100,000 items uploaded by its members and reaches about 100,000 visitors monthly.
EyeEm, pronounced "I am", is a German technology company that provides services related to photography. It was co-founded by Florian Meissner, Ramzi Rizk, Gen Sadakane, and Lorenz Aschoff in Berlin in 2011. Eyeem.com and the EyeEm mobile app offer photographers the ability to share photographs and discuss photography. The technology company uses artificial intelligence to find the images to license to brands, agencies or individuals. As of August 2016, the community had over 18 million users and more than 70 million photos.
Multiply was a social networking service with an emphasis on allowing users to share media – such as photos, videos and blog entries – with their "real-world" network. The website was launched in March 2004 and was privately held with backing by VantagePoint Venture Partners, Point Judith Capital, Transcosmos, and private investors. Multiply had over 11 million registered users. The company was headquartered in Boca Raton, Florida but moved to Jakarta, Indonesia early in 2012 and recently announced intentions to switch to e-commerce, dropping the social networking aspect entirely. Quantcast estimates Multiply had 2.47 million monthly U.S. unique visitors at their peak on July 30, 2012.
Licence laundering or license laundering occurs when a creative work under copyright is copied by another party, who then replaces the original licence with a different one. This party then illegitimately distributes the work with the new licence.
Content ID is a digital fingerprinting system developed by Google which is used to easily identify and manage copyrighted content on YouTube. Videos uploaded to YouTube are compared against audio and video files registered with Content ID by content owners, looking for any matches. Content owners have the choice to have matching content blocked or to monetize it. The system began to be implemented around 2007. By 2016, it had cost $60 million to develop and led to around $2 billion in payments to copyright holders. By 2018, Google had invested at least $100 million into the system.
Flickr enables users to post photos from nearly any camera phone or directly from a PC. It also allows users to post photos from their accounts or from their cameras to most widely used blog services. The result is that an increasing number of bloggers are regularly posting photos from their Flickr accounts.
For some of the details, we have 62 DBs across 124 servers- accounts are spread across 2 servers each. There are around 800k accounts per pair, give or take some thousand. On one of the pairs, there is a greater number of "active" members who populate it; stats recalculations have been taking some time longer to execute, and the database has not been happy.
In a similar move to harness the public's knowledge about old photographs, the Library of Congress a year ago began adding photographs with no known restrictions to a Flickr service called the Commons. The Library of Congress started with 3,500 photos and adds 50 a week.