Alternative to Google reCaptcha

Hey,

I’m using Google reCaptcha for the registration form (User Registration plugin) of my website. I just recognised that Google reCaptcha does not or really bad work if the user has disabled third party cookies.
Do you have any suggestions to solve that problem?

If not, is there an easy way to use another Captcha method in combination to your plugin?

Thanks in advance.

Best,
weekendize