@gaieus said:
No, the skp example was just an analogy. I mean to open the image in an image editor and start a new image in the editor, too. Then select the old image and paste it into the new one and try that new.
Gaieus, thanks for the suggestion. We "solved" it by starting a brand new drawing and inserting the images there. It plotted with transparency. What we didn't solve is why the problem with the first drawing? Corrupted perhaps? A mystery.
We also noticed in our first drawing that any text placed in paperspace, on top of the viewport, vanished in the plot preview and the plot. So we had 2 issues going on at the same time. It also wasn't a matter of plotting from paperspace. The subject image did also not plot transparent from model space.
Anyway we got the results wanted but still wish we could determine what was going on.
Thanks everyone.