If you need to take a screenshot on Raspbian you will find that the PrintScreen key does not work at all.
Here is a solution for that!
You will need a tool called scrot to take screenshots.
Install it by running the following on terminal:
$ sudo apt-get install scrot
To use scrot I like to use the following syntax:
$ sudo scrot -d2 -c -u [filename].png
-d2 means that the screenshot will be taken in 2 seconds;
-c means that there will be a count down on terminal;
-u means that the screenshot will be taken to the window on focus;
[filename] is the name of the saved file.
For more help with scrot:
$ man scrot