Ken Blake said:
Create a single graphics file that's made up of multiple pictures, and use
that for your wallpaper. You can do this easily with almost any image
editing tool.
Easily? Hardly. It would require creating one picture large enough to hold all of them, then opening, selecting, and copying the
first picture, pasting it into the big one, and repeating for each subsequent picture, making sure to precisely align each one. I
would hardly call that easy in any graphic editor (even ones that have nudging controls).
It's much easier to just let a program that's designed to do it take care of the work. Even the free IRFanView can make an index of
multiple selected pictures.