I think you need an additional tool to interface with the Windows Win32 GDI routines:

I would just install AutoIT3, and use their screencapture capabilities

And here is a guy that made a image resize, which you use after saving it to a temporal file.

I could not find additional libs in perl that had screen capture abilities.

In Linux, there are build in things, like xwd or ImageMagick to automate screenshots.