How to use it in ajax

Hello Horst,
so great to see that you still answering questions !!!

I used your fantastic class several times.

Now I want to use it with xajax.

In a normal not ajax envirnoment, I use it in the post section to verify the entered data like: if($sCaptcha->validate_submit()!=1)) {....} else {...}

How can I use it in ajax , which just is called via onclick (no submit).

Of course I have the field
<input type="text" id="hncaptcha_private_key" name="hncaptcha_private_key">
available in the xajax routine...

Q: How can I get the displayed characters displayed in the image, so that I can compare it in the ajax routine? Or any other function/possibility to compare without a submit?

Appreciate your help a lot.

Thank you very much in advance
Jack