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

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

The test is a multiple-choice question: "Click all the XXXs 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. However, due to the low resolution of the tiny pictures and ambiguous questions, like distinguishing between a squid and an octopus or boxes and containers, people have been struggling to answer correctly.

Since customers can only make a purchase after clicking on all the correct pictures, any wrong answers or refreshing of the Web page to get easier questions may cost users the chance to get a ticket.

Clearly frustrated, some Internet users edited the verification pictures to mock the system.

They created fake questions including "click on all the pictures of handsome men", "all cartoon characters who are short" and "all pictures of the Strait of Bosporus" to show how absurd the questions could be.

One potential buyer joked: "You know nothing when it comes to those pictures." Other netizens said: "Only straight A students could pass this," "I feel illiterate when I just try to buy a train ticket," and "Do I have to take an IQ test before buying a train ticket? ... Actually, I just want to go home."

China Railway, the authority of China's railway system, said on Thursday that it had adjusted the verification test to improve the images' definition and resolution. The test with the highest error rate and the most complaints will be removed from the system.

As people begin buying tickets for Spring Festival in February, more than 36 million users logged in to the website on Tuesday and bought more than 6 million tickets, according to Zhu Jiansheng, deputy head of the Computer Science Institution at the China Academy of Railway Sciences.

During the same period last year, 56 million people logged in on one day, although only 5.6 million tickets were sold, Zhu said.

"Fewer people logged in but more tickets were sold this year, which means there was less ineffective and repeated logging in," Zhu told Beijing News on Thursday.

Malicious software could verify the old code, which mostly combined numbers and letters, within 0.1 second, he said. So far, such software cannot pass the test automatically with the new code, he added.

It's becoming a fierce competition for people trying to buy tickets online for Spring Festival, during which billions of train journeys are taken every year.

Contact the writer at pengyining@chinadaily.com.cn