Why won't my wallpapers go into the wallpaper section in images, even if I select for them to be put in the wallpaper section?

An image has to be a standard wallpaper size in order for it to be accepted as a wallpaper - even if you're just a pixel or two off, it'll put it in the photo section. A few of the most popular wallpaper sizes are 600x800, 1024x768, 1280x800, etc.