A new study has suggested that dogs can tell the difference between our happy and angry faces.

Scientists from the Clever Dog Lab of the Messerli Research Institute in Vienna trained them to associate pictures of happy or angry faces with a reward.

In a follow up test, the scientists showed the dogs images of human faces they had not seen in training - suggesting that the dogs could spot the difference between the expressions.

"After learning to discriminate between happy and angry human faces in 15 picture pairs, whereby for one group only the upper halves of the faces were shown and for the other group only the lower halves of the faces were shown, dogs were tested with four types of probe trials," the lab said.

They were shown the same half of the faces as in the training but of novel faces, the other half of the faces used in training, the other half of novel faces, and the left half of the faces used in training.

"We found that dogs for which the happy faces were rewarded learned the discrimination more quickly than dogs for which the angry faces were rewarded."

Furthermore, it says the dogs performed significantly above chance level in all four conditions.

"We conclude that the dogs used their memories of real emotional human faces to accomplish the discrimination task," the lab added.

The scientists repeatedly showed 20 dogs half pictures of happy or angry human faces, as seen in this video: