(OCR ) How to Recognise Handwritten fractional numbers using Neural networks
Usually one of the steps is "segmentation", where we separate the image into smaller images, one for each character/symbol.  Thus the fraction "1/13" would have four character, "1", "/", "1", and "3".  Then, you apply a neural network separately to each of those four smaller images.

See https://en.wikipedia.org/wiki/Optical_character_recognition for an introduction.  OCR is covered in many standard sources.  I suggest reading the literature on the subject to learn more about standard methods.