You can also use a little program called YFSScreen, found
HERE.
You simply press "PrintScreen" during your flight and it saves the image to a predefined directory and the lets you keep flying. This way you can take as many screenshots as you want (up to 999) and then when you exit the sim you can sift through what you have and save what you want.
Just edit them to be 800x600 pixels, less than 100kb in size and ALWAYS *.jpg format and then upload them to SimV.
Travis