SAN FRANCISCO  Speculation in technology circles that Yahoo might close or sell Flickr, its photo-sharing service, prompted an emphatic denial this month.

“Is Yahoo committed to Flickr?” Blake Irving, Yahoo’s product chief, wrote in a message on Twitter. “Hell yes we are!”

The confusion over Flickr’s future was perhaps understandable. Yahoo had just recently disclosed plans to shut down or otherwise dispose of several other Web products, including the bookmarking service Delicious, and some users feared Flickr would be next.

A pioneer in combining photos with social networking features, Flickr is facing a stiff challenge from newer services. In addition to fighting rumors, it is having to work hard to keep its users returning as Facebook widens its lead as the popular destination for sharing party, vacation and family snapshots.