Asked by: James Malpas, Histon
On a website’s login page, CAPTCHAs are those obscure-looking characters we use to verify that we are human users and not bots. The characters are often distorted with the letters or numbers running into each other. Optical character recognition software struggles to pick out the individual forms, especially when their shape and size vary from one CAPTCHA to the next.
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.