Capturing is easy. You can use the gui, or just invoke the configurable hotkey. Lightscreen supports capturing full screen, window and area. The result will be automatically saved in a directory according to user preferences.
Besides, you can also choose between three different format of the output image. Lightscreen supports PNG, JPEG and BMP.
If you have any suggestion, please leave a comment.
Link: http://lightscreen.sourceforge.net/