GScrot is possibly the most comprehensive program I used to capture images on the desktop. Not only allows the screenshots but comes loaded with additional functions that in many cases are very useful. It is a graphical interface that works with scrot below, a far more limited program that runs on command line. It is available for GNU / Linux systems and integrated into the Gnome desktop.
Besides having a name that does not sound too well in Castilian, GScrot is able to capture the whole screen or just * * areas of it that the user select and take the picture specifying a delay in time. Allows you to set details such as keystrokes to make the catch, auto hiding at the time of the photo or keep it minimized in the notification area. The window is separated into three parts: the icons with the main actions, recording images taken at a meeting and finally settings.