I think people will get tripped up by you saying it "can't" be OCR'd or that it is difficult to do so, and will end up looking past a pretty elegant solution in

I think people will get tripped up by you saying it "can't" be OCR'd or that it is difficult to do so, and will end up looking past a pretty elegant solution in the process. This seems like a nicely clever way to trip up non-targeted scrapers which might attempt to OCR any images they encounter, but which will ignore what looks like random gibberish codepoints. It doesn't eliminate the ability to index this data but I can see how it might greatly reduce it. Obviously you could still convert these PDFs to an image and OCR them, but that's not the thing being defended against here.