What are ready-made CAPTCHA services for the site?

Question

CAPTCHA

Good day to all.
Tell me, what CAPTCHA service can be connected to a simple site? For example, in which you just need to enter letters or numbers from the picture or solve an example (there is a sample in the image). reCAPTCHA will not work, you constantly need to select images on it, and it doesn’t work the first time.

Answer 1

captchas.net
www.opencaptcha.com
www.protectwebform.com
textcaptcha.com
identipic.com
https://www.funcaptcha.com/
...
Google free captcha services
PS
Why do you need a third-party service? It's quite easy to implement, there are many ready-made libraries:
https://github.com/search?l=PHP&q=captcha&type=Rep...
The simplest thing that came to hand:
https://github.com/yasimturk/simple -php-captcha
https://labs.abeautifulsite.net/simple-php-captcha