I havent Found a File Approach to getting pictures off logon studio Vista but I have used print Screen But the problem with that is you can't use print screen when you are logged out (preview for Logon Vista)
One way I found out how to Get arount this and Extract Pictures from Logonstudio Vista is to Use annother Computer and Ultra@VNC
The VNC Program Is a Remote Desktop Program gives you the immage of the other computers desktop on your monitor
you can Download it from Sorceforge.com (i would add links but i am typing this on my phone)
Install On Both PC's and...
Run Server on the computer that has the Graphic Needed (comp a)
Run Viewer on the computer that you are using to get the graphic (comp 
In Server Set the password so you can Access this computer.
Once you see your desktop from Comp A on Comp B you may do the following.
Lock Comp a Using "winkey" and "L" (comp A)
There is a Point where you can print the screen before VNC will close (because it will when Comp A is Locked) You will have the full graphic But there will be The Windows Vista Tag at the bottom. It may take a few trys to get the timming right but if things go well you will get your image before you Logon Icon Comes on and your screen goes Black (vnc will go black when you lock the other computer) when this happens(if in fullscreen) press ESC. and your window will exit Full screen mode.
Also some video cards will not capture live images or streaming video. This way worked for me user results may varry. in such I am not responsible for any other complications you will have in capturing this image such as and not limmited to Compuiter Failure and Software/ hareware probs.
if this Does work for you...
for the best quality use the higest resolution (both Computers) and Full screen View on comp B. and HIGH SPEED CONNECTIONS between Computers will Impove image quality Too