Why can’t computers complete CAPTCHAs?

Why can’t computers complete CAPTCHAs?

Common CAPTCHAs have been around since 1997, but computers are a long way behind the human brain at cracking them.

Exclusive US Offer - try a BBC Science Focus Magazine subscription and get your first 3 issues for only $12.99 PLUS get delivery from the UK!

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.

© Getty Images

Sidebar Image

Exclusive U.S. Offer

Try a BBC Science Focus Magazine subscription and get free delivery from the UK!

Subscribe Now!
Want to keep up to date with the latest news from Science Focus?
By entering your details, you are agreeing to Science Focus terms and conditions. You can unsubscribe at any time.

Exclusive U.S. Offer

Try a BBC Science Focus Magazine subscription and get free delivery from the UK!

This website is owned and published by Our Media Ltd. www.ourmedia.co.uk
© Our Media 2025