Does a checbox provide an alternative to using captcha on website? I am thinking i i need to use captcha for user signup. Instead if i put a checkbox for the terms like "By clicking here I agree...." can that solve the bots issues or is captcha required in addition to the checkbox?
One thing you can do with a checkbox is to make a honeypot. To do so, you would make a checkbox and hide it with CSS (because bots, as a rule, don't care about CSS). If the box is checked, then it's probably a bot.
If you are trying to keep bots from signing up, they will be able to check the checkbox pretty easy. the point of the captcha is that it takes human intelligence.
No, bots can check boxes, use a service such as http://www.google.com/recaptcha to easily make a bot-proof form.
Not at all, a checkbox is just like any other input, which bots manipulate.
As recommended above recaptcha is good. I also like Akismet, which handles this completely different.
Checkbox Captcha generated with client-side Javascript can be an interesting option.
Check out that article published by UX Movement: "Captchas vs. Spambots: Why the Checkbox Captcha Wins" http://uxmovement.com/forms/captchas-vs-spambots-why-the-checkbox-captcha-wins).
This technique can work, but it is not too difficult to beat, given time and an interest in your specific site.
Using CSS and Javascript (which isn't completely accessible) to create the checkbox will defeat the more simplistic spambots. Also using a randomized name (which is verified server-side) for the checkbox POST/GET variable, and perhaps an image for the label (which creates more accessibility problems) will help make this more difficult.
In the end this should work fine, until someone takes the time to target your site or system specifically.
Edit The article linked to in this answer has good information.
来源：https://stackoverflow.com/questions/4028451/checkbox-as-alternative-to-captcha