In each step, the sheep were presented with two options: a photo of the celebrity facing forward for the camera, or a photo of something else.
Earlier studies showed that sheep can recognize their trainers' faces and the faces of other individual sheep in their herd.
It had been known that sheep can recognize familiar faces of other sheep and of humans.
For the initial training, the sheep received a food reward for choosing the face versus a blank screen. They were able to identify the faces of celebrities at different angles (although there was a decrease in performance of about 15%), demonstrating that they are not stupid. Researchers from Cambridge's Department of Physiology, Development and Neuroscience trained eight sheep to recognise the faces of four celebrities from photographic portraits displayed on computer screens.
"Humans do tend to underestimate the ability of sheep", Morton said by email.
Morton and her team are now studying sheep that have been genetically modified to carry the gene mutation that causes Huntington's disease. (A sheep might have had to select Emma Watson vs. a football helmet or gas lamp, for instance.) The third test pitted the sheep's celebrity targets against unfamiliar humans.
"Anyone who has spent time working with sheep will know that they are intelligent, individual animals who are able to recognise their handlers", said Prof Jenny Morton, who led the study.
Scientists aim to use the sheep as models to understand disorders of the brain, such as Huntington's disease, that develop over a long time and affect cognitive abilities.
The team got success after few days of tutelage of sheep at the Cambridge University in England, where at least 8 sheep could recognize Obama by his picture. "I guess they have extended our work to show that sheep generalize viewpoints of the faces, which does require a rich representation of the identity". The sheep chose the right face eight out of 10 times.
Likewise, when the authors of the new study swapped celebrity photographs with those of the sheep's handlers, the farm animals needed no training.