How to make the captcha on the page updated?

Question

PHP

Hello! I probably didn't state the issue correctly. But I will say here: I need my php to change when the page is updated (well, according to the idea, a new captcha was rendered), like this site arzkapcha.ru/kapcha.php . So, I want to create the same site, but not on the ru domain. (Because ore-domains do not work in Ukraine). I'll leave a link to the original site, don't worry :)