gImageReader is a front-end for Tesseract Open Source OCR Engine. Tesseract was originally developed at HP and then was open-sourced in 2006.
Basically, the OCR (Optical Character Recognition) engine lets you scan texts from a picture or a file (PDF). It can detect several languages by default and also supports scanning through Unicode characters.
However, the Tesseract by itself is a command-line tool without any GUI. So, here, gImageReader comes to the rescue to let any user utilize it to extract text from images and files.
See Use gImageReader to Extract Text From Images and PDFs on Linux - It's FOSS
gImageReader is a GUI tool to utilize tesseract OCR engine for extracting texts from images and PDF files in Linux. Here's how to install and use it.