The ksnapshot command is a versatile screen-capture utility. Simply run:

$ ksnapshot

and it takes a screenshot, displaying it in miniature. From there you can save it to a graphics file or take another screenshot. The file format will match whatever file extension you choose: .jpg to produce a JPEG file, .bmp for a Windows bitmap, .pbm for a portable bitmap, .eps for encapsulated PostScript, .ico for a Windows icon, and so forth. For a list of supported file formats, click the Save Snapshot button and view the selections under Filter. For more information, click the Help button in the ksnapshot window, or run ksnapshot --help-all from the shell.