My reading of that code (and I've never used any of the Win32 modules ever, so YMMV) was that you didn't press anything -- it simulated the keystroke for you.

The part I'm talking about is:

# press the key!!
$key->Call(0x2C, 0x45, 0x01, 0); #simulate a "printscrn" key press
$key->Call(0x2C, 0x45, 0x03, 0); # & release
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- Matt Riffle