There are many ways to take screenshots and most KDE and Gnome users will be familiar with the GUI tools bundled with them: Ksnapshot for KDE and Take Screenshot for Gnome. They are good at what they do. However, sometimes you just need to take screenshots quick and dirty without the overheads (especially if you are using a lightweight windows manager on a relatively low-spec machine). If that's your case, you can use “Scrot”.