Although the scope of the human users was limited, the results proved that robotic programmes were not able to recognise distorted images.

In other words, a computer recognition programme had to rely on an accurate picture, while humans were able to tell what the picture was even though it was distorted.

Wang said he hopes to work with developers in the future to make IMAGINATION a CAPTCHA programme that websites can use to strengthen the prevention of automated network attacks.

Even though machine recognisability does not exceed human recognisability at this time, Wang says that there is a possibility that it will in the future, says a PSU release.

These findings appeared in the September issue of IEEE Transactions on Information Forensics and Security.