NOW THAT I HAVE YOUR ATTENTION...
...Yes they are allowed by the rules as long as they don't have HUD or bad quality.
I find game screenshots worthless (and I do like video games) but they seem like a dumb thing to put as a desktop background. They are not "specially made" they are just a static moment on a game, they are not thought as art in its conception, just a representation of something that some people seem to identify with, more like a brand logo. Even high res screenshots are just game screenshots.
The quantity of these are growing day by day and if you add the people that tags these images so specifically to the mix (by tagging them as the game title only, instead of adding "video game" as a tag) makes it really difficult to filter.
PLEASE IF YOU ARE GOING TO UPLOAD SCREENSHOTS USE THE "VIDEO GAMES" TAG.