That looks more like pecking injuries. Also, full grown chickens are fine in cold well below freezing, as long as the coop has adequate ventilation. Heat lamps are also a fire hazard, so I'd be hesitant to use them- save 'em for the chicks!
Edited to add this from My Pet Chicken:
The inexpensive, 250-watt infrared heat bulbs you'll find in any feed store or retail outlet are super dangerous. They put out 435° plus temperatures, making them an especially risky way to heat your coops and brooder because they're dusty places to begin with, and bedding is quite flammable. If you
must use a heat lamp, double and triple check that you are not creating a
fire hazard. And then just to be sure you're safe, throw the darn thing out. They're just that dangerous. ...
If you have special needs birds or your area regularly sees temps below freezing, you may indeed need to give your flock a little heat boost to help them through the winter. For that, there's nothing better than the
safe, energy-efficient Sweeter Heater, the low-wattage
Cozy Coop Heater, or
Thermo-Peep Heated Pad.
These heaters won't heat the whole coop; they'll only provide a little extra heat on contact, when birds snuggle right up next to them. This allows your birds to still acclimate to the colder weather, while providing potentially life-saving warmth during especially cold snaps.
Whatever you do, just remember: DON'T HEAT YOUR COOP WITH HEAT LAMPS!
I have the Cozy Coop Heater, and love it.