On several separate occasions I tried to use Tesseract to OCR base64 and similar text that was printed in a normal monospace font (i.e. not a special OCR font) and scanned.
I never got even close to getting useful results. I tried limiting the alphabet, disabling language models as far as I could and at most I could get a few recognizable character sequences right out of the whole page. I got the impression that the whole thing very much depends on being able to split text into English words and have easily separated paragraphs.
I might play with Tesseract[1] this weekend and see if this is even a feasible idea. If so, it makes the paper key storage a lot more palatable.
[1]:https://github.com/tesseract-ocr/tesseract