The OCR Image action allows you to extract the text from an image using OCR (Optical Character Recognition) (specifically using the Tesseract OCR library).
The source image can be pasted into the action, or read from the System Clipboard, Trigger Clipboard, a Named Clipboard, or a file, or you can get the image from the screen.
When reading from the screen, you can get the image from all screens, or from a specific screen or window or area on the screen.
You can choose what language or script the text is in. Each language will require a download, typically between 1 and 10 MB, though there are a few scripts that are significantly larger.
As with any OCR, the text may contain errors so you should be careful not to assume the result is 100% accurate.
Note that the Tesseract OCR software prefers black-on-white text, and while it will often work with white-on-black text, it will be more likely to fail in those cases.