How to submit data to captcha form with static URL using C#?

Question

C++ / C#

I have an HTML form. A captcha is attached to the form, its image is sent to the static address img.php .
It is required to write a program that every n minutes sends a message to the form, but before that shows the user a picture with a captcha and requires him to enter it.
What is the right way to take a picture? Need to open a hidden browser window?
Tell me, in which direction to dig-google?

Answer 1

HTTP requests and the Fiddler sniffer.

Answer 2

WebClient HttpWebRequest Cookie Html parser, if necessary
Requests can be viewed in the developer console or in the sniffer