What is the algorithm behind OCR?
Probably the simplest OCR algorithm would be the case where the characters are from a known font, in perfect rows with no distortion or rotation, and then you can find occurrences of each character in the text by doing cross-correlation with the known characters from the known font.

Or even simpler if you can create the font before it's used, with cheaper ways to recognize characters, like the MICR fonts or OCR fonts.