I have been using Picasa http://picasa.google.com & Picasaweb http://picasaweb.google.com to identify old photos that were in my grandmother’s trunk, and it has been a great success.
Any online photo gallery will work here. All I did was upload my photos to a public gallery & email a link to the site to relatives. Then ask them to try to identify the pictures, also ask them to let any of their relatives know about what I’m doing.
The only problem with Picasaweb was there was no way to edit comments, just delete them.