Seeking advice on building large-format montage

[qwert]

I'm looking for ways to construct a large-format montage of images using AutoIt.  My first attempt encountered the limitation for the size of a single window ( [12+@DesktopWidth] x [12+@DesktopHeight] pixels.)  My inclination is to make the "interior" of a max-size window scrollable, and then move around to place individual images with GDI+ calls.  But that leads to issues like how grab the resulting 5000x5000 image so it can be pasted into MSPaint for further edits and printing.

Ideas will be appreciated.  Thanks in advance.