There will be a My Photos section in the game. When you open that up, it will show you all of the pictures you took. Find the one you want, press triangle, and select Export to XMB. Quit the game, and go to the Photos section on the XMB, and find the picture. Connect a flash drive to the PS3, press triangle when you found the picture (do not open it) and select Copy, then Press X when it shows the flash drive.
If you want to do multiple pictures, a quicker way to do it is while in the game and have the My Photos window open, hold the L1 and Press X to select the photos you want, and while holding L1, press triangle and Export to XMB. Quit the game, and find a photo in the XMB, press triangle, and choose Copy Multiple. Press X to select the photos you want, and export them. Remember to select Rename and Save when prompted. Hope this helps. Message me if you need any further assistance.
