Slackware :: Way To Print Photographs ?

I'm working with two systems (mine and somebody else's) trying to print photographs -- trying is the right word, too. Both boxes are Slackware 13.0, both printers are H-P Photosmarts (a 3210 and a C4680), both systems have the latest and greatest HPLIP and CUPS software installed and both print everything else just fine. Photographs? Well, nuts: can't figure out how to get an image printed on standard 4x6 stock (meaning: fit or fill the image to the stock). Been fiddling with HPLIP settings, CUPS settings, fooling around with GIMP, twiddling everything I can come up with and there is no joy in Mudville to be had. About as close as I've gotten to, you know, a printed photograph that looks like a printed photograph is supposed to look is setting HPLIP options then printing with lp file.jpg but that doesn't actually work all that well.