You’re trying to book concert tickets before they sell out. You click the link and before you can make the payment, you’re asked to identify traffic lights, bicycles or blurry crosswalks in a grid of tiny images.

For many people, this has become a routine part of life. Logging into financial apps, shopping online or creating accounts increasingly involves “proving you are human”.

These systems are known as CAPTCHA. Why are they everywhere?

The short answer is that websites are fighting a rapidly escalating war against bots: automated software that imitate human behaviour online. And thanks to advances in artificial intelligence (AI), those bots are becoming even smarter, cheaper and harder to detect than ever before.

Why websites need proof you are human

Huge amounts of online traffic now come from automated systems. Some are helpful, such as search engine crawlers indexing pages for Google search.

Others are far less welcome, and may involve phishing, spam, fake accounts,........

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