The heads on most printers are notorious for accumulating dried, gummy ink. The result: streaks, dollops and smudges of ink on anything that comes out of the printer. The Officejet K7100 model, manufactured by Hewlett-Packard, is a photo printer susceptible to this issue just as much as any other printer. While the printer software has a "clean" feature on it that might help tidy the heads, in most instances the best way to clean a photo printer is to manually take out the heads and clean them yourself.
Put plastic gloves on your hands to keep ink from getting on your skin. Cleaning the heads of most printers can prove to be a messy process.
Carefully take the ink cartridges out of the printer.
Pour a small amount of the rubbing alcohol or glass cleaner onto a paper towel that has been folded twice. It needs to be moderately moist.
Wipe the bottom of the cartridge -- the area containing the print head--onto the moist paper towel. Repeat the wiping process until all gummy ink is gone and the head is clean. Clean ink will flow from the ink head.
Replace the ink cartridge in the printer.