Is it possible to take screenshots in Skyrim on the PS3?
Solution 1:
There's kind of a roundabout way of doing it, by saving your game and then copying part of the save over to your computer (source #1, source #2):
For PS3--First, save your game looking at what you want to take a screenshot of. Then, copy your save file onto a USB stick and open ICON0.PNG on your computer.
The resolution of this "screenshot" is rather poor though: 320x176
Beyond that, I think you'd probably require some type of HDMI capture card in a PC, which is an expensive and kludge-y solution. I have a friend who has a high-end rig with one of these, and he uses it to take Xbox 360 videos and screenshots pretty frequently.
Solution 2:
Some support is offered when USB Keyboards are plugged in, but I don't think Skyrim supports it on PS3.
ANOTHER option however (if your PC video card has S-Video in) would be to play the Ps3 while attached to your computer, than use something like Nero or attempt to take screenshots while output to the monitor. That by far is probably the best way, and how most people record gameplay.
So to repeat, good video card with input processing, then capture / save the screenshot on the PC. But really to be frank, at this point you might as well get Skyrim for PC and save the money (if you don't have a good enough video card).