So here we have some suggestive evidence that they interpret those pictures, and maybe they really understand an angry face to be something they don't like.

Half the dogs received a treat when they touched an angry face with their nose. The other half were rewarded for touching happy faces.

Here, I added some quick color overlays and some glare to the left. This step only took a few seconds but amps up the atmosphere of the image and brings in a little warmth.