The gallery avatars do not go directly into the gallery directory.
Lets say you had cat avatars they would go in images/avatars/gallery/cats
and dog avatars would go into images/avatars/gallery/dogs
If you did not do it that way then you could not have different categories for the avatars - they would all be mixed up. And anyway phpBB2 will not let you put gallery avatars in directly. They must be in their own directory inside the gallery one.
The truth is out there.
Unfortunately they will not let you anywhere near it!