I cannot for the life of me get this to work. Here's what I'm doing:
The problem was with the images. I haven't been able to figure out exactly what was wrong with them. Resaving them with a different editor caused them to start working in my project.
In case it helps anyone, these were the details of my scenario:
pHYsdimensions were different between the good and bad files (good:
00 00 0B 12, bad:
00 00 0B 13, which both correspond to 72 dpi). Obviously DPI shouldn't matter here, but I do vaguely remember a case where I had trouble with images that didn't have a certain DPI written into them in the past.
At any rate, I dearly hope this saves someone else some hair pulling.