A group campaigning for banks to make online services more accessible for visually impaired customers has renewed its call for regulating authorities to look into CAPTCHA codes.

CAPTCHA, short for "completely automated public turning test to tell computers and humans apart", refers to the blurred codes Web users must enter before they are allowed to confirm a function, such as registering an account or completing a transaction.

They are used to prevent malicious attacks by hackers and "bots" - computer programs designed to spam websites - and many Chinese websites use them.