In case anyone is still interested in overlays, I've finally got it working - thanks to Karibou in the DAZ forums, who figured it out.

I was using a Color Math node to overlay multiple inages on a black page texture. Karibou discovered that only works with a white background. But it can be done using the basic image nodes, setting Image_Mapped to Alpha, and connecting the last (black page) texture to the background of the photos.

Using that system, I've successfully overlaid 3 images on the page, and I can add as many as I like.

I'm attaching a screen of the nodes, although I'm not sure if it will upload.

mac

Nope - As I thought, every time I try to upload a pic of the material room, I get the Amazon S3 error

I'll try to explain it verbally.

Image_Map1 (photo 1)> Diffuse Color

Image_Map2 (photo 2)> Image_Map1 Background - Image_Mapped = Alpha

Image_Map3 (photo3)> Image_Map2 Background - Image_Mapped = None

Image_Map4 (black page paper tex)> Image_Map3 Background

Obviously, each photo node needs to have UV Scale/Offset tweaked to get the position right. Image1 will be above Image2, etc, so you can actually set the order and have one photo partially cover another.