First, I would like to say that I do not speak English fluently, so sorry if there are errors in this post
What I will be teaching now is not exactly a screenshot, but I believe it is best we can do on ps3
When we save a map, will appear in his save a screenshot of the last part before the save, and it is what we use.
Like I said you will need to save your game so that you can have your screenshots and you will obtain them (this part you need a pendrive):
Ps3 Menu> Games> Saved Data Utility
There appears will save your screenshot and it will save and press the triangle Then several options, choose "copy" (It will appear the symbol you have to be a member of playstaiton plus but dont need)to (your pendrive).
Then open your pen drive on your computer and open the "PS3" then "SAVEDATA" folder and it is your will saves, click the save that your screenshot.
The screenshot will with this name ICON0
Now remember that to get more screenshots you that you will save your game
Now I will show you some screenshots of a map of minigames that I am producing