A snapshot of the verification test requiring customers to click all the lizzards in the pictures. [Photo from web]

An online verification to buy railway tickets has turned the process into an intellectual challenge, meaning customers must be Internet savvy with fast clicking fingers, sharp eyes and a quick mind.

12306.cn, the only official website in the country allowed to sell train tickets, has been receiving numerous complaints about the verification code test users must pass to buy tickets online.

The test is a multiple-choice question: "Click all the XXX from the pictures below" requiring customers to match images to descriptions of things such as recorders, electric generators, fans and humidifiers.

The security check is meant to prevent auto logins or malicious purchasing by machines. It is supposed to be an easy way to tell if buyers are human or machines, but due to the low resolution of the tiny pictures and ambiguous questions, people have been struggling to answer correctly.