Ugh - Images display just fine in the context of my albums, but when a user clicks an image to get the full size version, they get a 404. For example:
http://www.derekandcristina.com/photos/albums/abbyjosh/IMG_1792.JPG

That link will result in a 404, yet I can ASSURE you that the file does exist in that location on the server. What's interesting is that my other albums don't have this problem...

What the heck is going on?

Err, my bad. Permission on the album directory was for Group and World Read, but the individual files did not have the right permissions.