How does the server know that the captcha is solved correctly?

Question

CAPTCHA

I'm trying to find a way to solve a captcha. To do this, I need to reproduce the same captcha. what is shown on the page to solve it. I can't figure out how to do it. The link to the captcha is general and returns a new captcha with each request - Capthca Link
There are no special cookies or other IDs in the headers.

<td class="formbg2">
         <label for="pwd">Enter Below Captcha<span style="color:red;">*</span><br>
   
            <iframe align="center" name="frame1" id="frame1" width="175" height="60" border="0" frameborder="0" src="/APCARDECClient/simpleCaptcha.jpg" marginwidth="0" marginheight="0" target="_self" scrolling="no" style="width: 129px;
    -webkit-user-select: none;
    height: 36px;">
                          
                          </iframe> 
                          <a id="docIdAch" onclick="return DrawCaptcha();" href=""><img src="images/refresh.png" width="30px" style="margin-left: 3px;
    margin-top: 2px;"></a>
    </label>
     
    </td>

How does the server know that this particular captcha is correct? Should there be some kind of ID?

Answer 1

When a captcha is requested, a session identifier is transmitted in cookies, a captcha image is generated on the server, and the response is written to the session data stored on the server. Every time you request another captcha, the answer to it is updated in the session data.