Tesseract is the OCR engine that helps to recoginze text. Google now maintains the project.
You can use Tesseract on iOS too.
I forked the github project because the original has a couple of problems compiling. To be precise:
File is universal (three slices), but it does not contain a(n) ARMv7-s slice for ..
This is because the original project was 10 months ago, and did not support for armv7s (iPhone 5). You can hack a build by yourself.
But I have fixed that for both tesseract libs and also updated opencv2 libs.
For your convenience: https://github.com/samwize/iPhone-OCR-Tesseract-and-OpenCV