By default printscreen or alt print screen will get the whole desktop or the application in focus, respectively. But what if you want to select a portion of the screen?
gnome-screenshot:
ksnapshot
compiz
This is a nicely integrated solution
sudo apt-get install compizconfig-s........
gocr works great and it's simple, just invoke it like so:
gocr filename.png
The output will be printed to the screen.
My only complaint/concern is that even with standard terminal output (not scanned) from a printscreen, gocr does make mistakes by inserting extra spaces where they don't belong, mistaking letters for numbers etc.. but it's definitely enough to be readable and figure out what you're looking at.
I haven't tested yet with scanned input........