I remember when OCR of mathematics was such a difficult problem that there was no good solution. I remember hints some years ago that the then-current version of InftyReader could do a reasonable job of taking a PDF document and converting it into LaTeX code, but it was far from perfect.
Today my phone told me that the app Photomath has an update and now supports handwriting recognition. This means I can write something like this:
and Photomath does this with it: