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. Reception 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. Controversies Censorship 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