1. A CAPTCHA method executed by a CAPTCHA system, comprising: receiving a CAPTCHA request comprising category information of an application service from an application server; responding to the application server with a token identifying the CAPTCHA request and a CAPTCHA image comprising a distorted advertisement word associated to the category information and a series of randomly generated and distorted characters, both the advertisement word and the characters being a CAPTCHA text intended to be typed by a user via a user equipment connected to the application server; receiving from the application server the token and a CAPTCHA answer submitted by the user; and verifying the token and the answer and returning to the application server a result of the verification.
1. A CAPTCHA method executed by a CAPTCHA system, comprising: receiving a CAPTCHA request comprising category information of an application service from an application server; responding to the application server with a token identifying the CAPTCHA request and a CAPTCHA image comprising a distorted advertisement word associated to the category information and a series of randomly generated and distorted characters, both the advertisement word and the characters being a CAPTCHA text intended to be typed by a user via a user equipment connected to the application server; receiving from the application server the token and a CAPTCHA answer submitted by the user; and verifying the token and the answer and returning to the application server a result of the verification. 9. The method according to claim 1 , further comprising: receiving, at the application server, a request for a web document from a client browser; in response to receiving the request for the web page, transmitting, from the application server to the CAPTCHA system, the CAPTCHA request comprising the category information; receiving, at the application server, said token and said CAPTCHA image; and after receiving the CAPTCHA image, transmitting to the client browser the requested web document, wherein the web document causes the browser to display the CAPTCHA image.