Linux OCR(optical character recognition) programs
How to prepare image to convert
Tesseract OCR: Installation and Usage on Ubuntu 16.04
Other links
Comparison of optical character recognition software
Free OCR Software (Optical Character Recognition)
What are the best Linux OCR programs?
Tutorial: How To Extract Text From Images on Linux Using Tesseract-OCR
Tesseract Command Line Usage
OCRmyPDF adds an OCR text layer to scanned PDF files, allowing them to be searched