3rd key from the right, top row. "prtscn" or some such, it varies.
When you hit that key it copies the screen, just as if you were using copy function in a document.
Then open a word processor or an image editing program and use the menu to "paste".
Save it and you have your proof.
Then make another, paste it in, etc etc.
There's also a program called snaggit that lets u scroll entire lobbies and capture the whole thing as a single file.