FPAlbum is a free web-based album software which let you share your photos or images with others.
You can have a public album which share the photos with everyone, or a private album which share the photos with your friends only.
You can change the style of the album using XSL.
WordPress user can also share their photos in their blog using the new wordpress plugin!
The project officially started on 12/10/2005 by Kevin Lam. See my (boring) blog if you want.
FPAlbum page in sourceforge.net: http://sourceforge.net/projects/fpalbum/. Please feel free to ask in the forum.