You can practice with these user pictures for the "External picture" option in the 7 style skin.
It's not that hard to take any picture you have and use practically any photo program.
Just crop it as a square, then reduce size to 48x48 pixels, 60x60 pixels, or 72x72 pixels. 

48x48 pixels for 100%/96dpi Windows display size
60x60 pixels for 125%/120dpi Windows display size
72x72 pixels for 150%/144dpi Windows display size

Don't be alarmed if menu shows as white menu. That can happen if the image got renamed or moved.
If this happens, just put a new location, or select one of the other picture options to clear it. 