I have a Tk gui that generates several plots and graphs using the Tk::Canvas. Currently, I allow users to save .gifs, .pngs, .jpegs, etc by converting the canvas to GD, then dump to disk. Several users have asked that I allow them to CNTRL-C the canvas image (copy to clipboard) so they can paste the image into an email, spreadsheet, whatever. It's really more of a convenience... they already have the ability to get the image from the disk save.