Pingback (callback) on 2capcha.com

#1
We provide a pingback (callback) option that allows you to get the answer for your captcha automatically when it's ready.
It allows you to get answers without making requests to https://2captcha.com/res.php and also allows you to avoid account suspension.

To receive automated pingback you have to:
Register your pingback domain/IP address.
Provide your pingback URL as a value for pingback parameter of your request to https://2captcha.com/in.php.
Process HTTP POST request with URLencoded form data (application/x-www-form-urlencoded) coming from our server to your pingback URL. The request contains two parameters: id - captcha ID and code - the answer.

Incoming pingback request example:
Code:
id=51555263943&code=ANSWER
You can use any pingback URL pointing to your registered domain/IP address so your URL can include custom parameters.
But there's one limitation: if you will submit your captcha with GET request and use URL that contains multiple parameters like http://mysite.com/pingback/?myId=1&myCat=2&something_else=test then you will receive pingback to URL with only the first parameter ?myId=1. To avoid that use POST request with multipart/form-data.