You can sorta' kinda' do a photo gallery, but it's not what vBulletin was built for. You can attach photos to posts, and reference images from another Web site. A photo album program will include a thumbnail gallery; click on the thumbnail, and you get a the full sized photo.
You can theoretically post huge images here, however, I limited the maximum size so it doesn't bog down the loading of a message thread. People expect a photo gallery to be graphic-intensive, so they're more patient with loading speeds.