My own website is slated to use captchouli at some point in the future.
You can also use a hidden input field that a user would never interact with, but a bot would send an input to. Then you can safely block all requests made from that input field.
That's hardly foolproof, but the only reliable ways that I know of that do not require user input are JS-based and make determinations using analytics. So basically, what you're asking for is botnet.
captcha is heinously anus
> captchas that don't require user input
OP, what do you think a CAPTCHA is, just curious
>>5
i think he means text input... not that multimedia captchas are any better. i would much rather have a lightweight textbox like on here than google's horrible mess
What about hcaptcha
>>7
ECCHI-CAPTCHA, identify the slutty femboys in this image.