On my system I use a little script coupled to a key that lets you select a graphical area with text in it and it converts it into real text that is placed in the clipboard:

#!/usr/bin/bash

maim -us | tesseract --dpi 145 -l eng - - | xsel -bi

[[ "$(xsel -ob)" ]] || (notify-send "No text found"; ohno)

You wil have to install maim, tesseract and xsel for it to work.

Edit: you can leave out the ohno which is just an audible alarm on my system