Yahoo is shutting down Yahoo Photos — for years, the No. 1 or No. 2 most-visited photo site on the Web. Its users will be directed to move their pictures to Yahoo's hot upstart, Flickr.

Flickr, acquired by Yahoo in March 2005, has steadily gained traction. Visitors rose 22% between April 2006 and April 2007, according to measurement service Hitwise. At the same time, Yahoo Photos lost 60% of its audience.

In its heyday, Yahoo Photos was such a go-to place for photo-sharing that more than 2 billion images are stored on its servers, to nearly 500 million for Flickr.

Yahoo Photos will be shut down by the fall. Users will be directed over a three-month period to transfer their images to Flickr or other photo sites such as Shutterfly, Kodak Gallery, Snapfish or Photobucket. Yahoo says it will make the transition easy, with a one-click transfer process.