OCR stands for Optical Character Recognition. It's the technology that looks at a picture of text — a photo, a screenshot, or a scanned page — and figures out the actual letters and words, giving you real text you can copy, search and edit.
Without OCR, a screenshot of a paragraph is just pixels: you can see the words but you can't select them. OCR extracts the text so the content becomes usable.
You can extract text from an image right in your browser — nothing is uploaded.