The photo thing might really work!Maybe do an impression in clay? I don't know of any bird-safe inks or paints, or even clays for that matter! But.. it's an idea. Or take a photo and digitally manipulate it?
Hmm.. maybe get him to stand on a glass table? That way the pressure is right and maybe the photo can be adjusted to look like a footprint.
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I tried it on my Guinea pigs first, but it doesn't want to adhere to the foot well.