Isn't that situation a good place to use QR codes? It might be a large code (im not sure the limitations of QR codes) but it would eliminate the need for OCR. Nobody is going to be decrypting it by hand so you don't really need letters that are human readable. The base62 form works well for posting online but for printing QR seems like a good format to me
So QR codes are great as part of a designed workflow where the reading app is well understood. The challenge comes in more ad hoc scenarios.
Also QR codes hit a certain practicality limit with size (2953 bytes to stay in spec)
Perhaps a meta-point is that when you are trying to design a general purpose interchange format, there will always be scenarios that you didn't imagine. In this case I have raised OCR and (legitimately) many people's responses have been a rather polite WTF (although I did garner one downvote). Experience teaches us that formats will be used in unexpected ways.
