Two pictures in Header instead of one?

I have a large number of identically-sized images in the header directory, and they're all square.

I want two of them displayed in the header image area. It's irrelevant if they're random or sequential, but they should change at each page change.

I searched and saw nothing that matched exactly. I don't want to have to make a bunch of "two-pics-merged" in Photoshop, so am wanting to do this with a code block, if anyone has one that will do what I need.

Nothing fancy, just two side-by-side images from the header directory, instead of one.

Thanks in advance!

And if I've missed something obvious, mea culpa.