OCR stands for optical character recognition. 'What does that mean?' you ask. Just think of OCR as computer software that can scan a piece of paper for you and type in what it says. Remember that snapshot on your cellphone with a picture of the chalkboard for this week's homework assignment on it? OCR can translate the image of the teacher's words into a text document for you. That saves a lot of typing.
For the most part, anything which can be scanned into a computer file (a fax, a photograph, a snapshot of a check or money order, or even something done on a typewriter which has been scanned into a computer), can be read by OCR software. It's not always great at getting the words right, but often it does.
Pictures versus Computer Files have you heard of microfilm? Microfilm is a tiny strip of photographic film with tiny pictures on it. Once upon a time (before computers), this was the most efficient way to store information. You just took a picture of a big newspaper and shrank it down to a tiny picture to save space.
If you needed to look it up again, you put it in a microfilm reader and manually searched for whatever you needed. Computers have changed how we store and search for information. Computer files save a lot more space and make it a lot easier to search for stuff, too. Nowadays, most images and text are stored in computer files.