Washington, Sep 10 - Computers can copy many aspects of human behaviour, but they don't yet possess our ability to recognise distorted images, says a team of researchers.

'Our goal is to seek a better understanding of the fundamental differences between humans and machines and utilise this in developing automated methods for distinguishing humans and robotic programmes,' said co-author James Z. Wang.

Wang is an associate professor in Penn State University (PSU) College of Information Sciences and Technology.

Wang, along with Ritendra Datta, a PSU doctorate and Jia Li, associate professor of statistics at Penn State, explored the difference in human and machine recognition of visual concepts under various image distortions.

Researchers used those differences to design image-based CAPTCHAs (Completely Automated Public Turing Test to Tell Computers and Humans Apart), visual devices used to prevent automated network attacks.

Many e-commerce websites use CAPTCHAs, which are randomly generated sets of words that a user types in a box provided in order to complete a registration or purchasing process.