What format should be used for school books that can't be OCR'ed?

[Mastiff]

I'm working on a setup for scanning the kids' school books, but I have found out that there is one type of book that I can't do the regular way (with OCR): Math books! Because one number wrong will mess up too much, and because the OCR software obviuosly have problems with those, I need another solution. The two things I need are:

1. Readable on an Adam (Android tablet).

2. Possible to write notes and mark text (but of course not as text since this will in fact be pictures).

Number one is easy, but number two is a bit more complicated, it seems. Regular image viewers can't do it, and advanced viewers usually only makes notes about a picture (meta notes), not directly on them. So is there anything I can use that will work this way?