I have noticed that sometimes when I upload a pic into a gallery, it says that it uploaded successfully, but when I go to check out the picture, it's a dead link.

I figured out that the files that this was happening to had filenames that are too long.

Shorten the filename and you're good to go.

Please note that when you go to delete the dead picture, it will tell you that it was unable to delete the photo, but it will delete it from showing in your gallery, so don't mind that notice.  This is simply due to the fact that the picture cannot be found because it didn't actually upload due to the filename issue.