Google Picasa Web Albums now recognizes faces in photos, the new version is live now, you can try the name tags feature here, or go to your picasa page you will see a notification for the same. Along with picasa web albums Picasa 3.0 desktop software also got this feature.
The facial recognition technology is called “name tag” that will help you to quickly label people from your photos. You have to Opt-in to name tag feature to use it, once you are in face recognition technology automatically groups photos containing similar faces. Instead of tagging each photo this technology allows you tag many photos at once.
Instead of asking you to painstakingly label pictures one-by-one, name tags lets you rapidly tag many photos at once. By doing so, you can easily find that photo of your cousin from two years ago; create a slideshow of you and your best friend, or share an album with everybody who appears in the photos.
more at Google Photos Blog, via CNet
