Very minor but interesting nitpick: the font used on checks is not OCR (optical) but MICR (magnetic ink). The design objectives are different and different font families exist for the two purposes. MICR as used on checks (more properly called E-13B) bears unusual, distinctive character shapes emphasizing abnormally wide horizontal components due to the need for each character to have a distinctive waveform when read as density from left to right, essentially by a tape recorder read head. Fonts optimized for OCR are usually more normal looking to humans because they emphasize clear detection of lines instead.
E-13B is a bit of an ideal use case for this method because of the highly constrained character set used on checks and the unusually nonuniform density of E-13B. The same thing can be done on text more generally but gets significantly more difficult.
https://lifehacker.com/how-to-uncover-blurred-information-in...