OCR needs to be standard in all PDF documents. If some documents have been scanned or photocopied multiple times and it's hard to identify the images or the text is hard to recognize with OCR, there should be a banner that says something like "We recommend you use a different copy of this document as it is no longer up to accessibility standards."

Jus to clarify teachers/professors who are transitioning their handouts to digital will often scan in their overly photocopied documents which are hard to make out the pictures and could be hard for OCR to identify text (not sure how OCR works when trying to identify text). Their are also annotations that make it hard for OCR to make out too.