A new optical illusion is so good that it has fooled Google's reverse image search algorithms.

The photograph, shared on Twitter, confused tens of thousands of people.

It is of a cat with its head tilted sideways, in a way which makes it look like a crow.

The photograph was shared by Robert Maguire, a Research Director at Citizens for Ethics, who wrote: "This picture of a crow is interesting because...it's actually a cat."

It has since amassed more than 35,000 retweets and over 100,000 likes.

When the photograph is submitted to Google's reverse image search tool, it says it is a "common raven."