And the interesting thing about that is, you'd think it would be (relatively speaking) straightforward for Google to keep track of the first place a given image

And the interesting thing about that is, you'd think it would be (relatively speaking) straightforward for Google to keep track of the first place a given image was indexed (or possibly the first few places, or everywhere it was seen over the first X period of time since you couldn't guarantee the very first would always be the original). Assuming that original was still online, it would seem to be the place to direct searchers to, regardless of pagerank or whatever.