OK, so instead of marking a wallpaper for deletion in order to report that it is in the wrong category, let's use this thread as a means to report those cases.
[color=#FFFF99]One simple rule:[/color] Enclose the Wallpaper ID in square brackets [ ] when reporting so the wallpaper thumb is visible, and mention what category you think they should be in.
Wallpaper ID is present in the link for the wallpaper.
Example: http://alpha.wallhaven.cc/wallpaper/253702
In this case, 253702 is the wallpaper ID. Enclose that in square brackets and you get this: