This tiny python script puts all your steam screenshots in folders named after the game. Just execute steam-screenshot-sort.py in the steam-scrreenhot-folder (f.e. "C:\Program Files (x86)\Steam\userdata\[xxxxxxxxx]\760\remote").
The alternative script "steam-screenshot-sort - user folder.py" can be placed in the user-defined screenhoot folder (see Steam > Settings > In Game > Screenshot folder), and also sorts the pictures in seperate folders.