Yes, the number of spammers decreased a lot when we added the captcha. TRhen we took it away to make it easier for the students at the rena summer school. And for about a week the spammers did not notice. Then one day we had 200 people joining with random names, randome email and ALL THE SAME password. Those were easy to find :-).
We put back the captcha. But yes, we need to integrate this API