I figured it out. I was right and Vortex is wrong. Even worse is Vortex's error message is wrong. There isn't anything wrong with having images in fomods. The fomod in question had 199 other image links that worked just fine. Just 20 of them didn't.
If a FOMOD has conditionFlags between the description and the files then the image line has to be above it, for absolutely no reason other than Vortex doesn't like it. MO2 doesn't care what order you put them in, only Vortex.
