Captcha and ReCaptcha are great services that work well and are very well known. I personally don’t tend to like them much since the words or numbers to type can be so hard to recognize that it’s almost impossible to get it right. Sometimes it’s so hard that it is impossible. Well there’s many other solutions available to for forms, comments, and trackbacks.
1) Honeypot is a way of having an additional form field on the web form that’s not visible to browsers. CSS is used to hide the form field and if it’s filled out then the form system marks the full form information as spam. It’s handy and can help prevent a good amount of the spam a web site owner would get from a form ie. a contact form, a free quote form, and etc.
2) Askimet is the most popular way to combat spam. It searches for keyword matches, gibberish text, links to shady web sites, and such. None of that Buy NFL Jersey’s comment spam will get through Askimet. I highly recommend it.
3) Math / Quiz questions – They are popular and aren’t very hard to implement. They are an extra field to fill out but I think most people are used to fields like that and having to fill them out to prove that they are human.
There’s plenty more options and I’m always looking for new ways that are user friendly. If you know of any please feel free to leave a comment below with your spam killing suggestions.