One of the problems with images and captcha technology is usability. Visually impaired users can not view the text in an image and in many cases can not get past a CAPCHA form. I have not experienced spam coming through a secured form, and by secure I mean with no viewable e-mail address and extensive input validation.

I also think that obsfucating the e-mail address using some type of encoding is effective. It is not commonly done right now, so most bots don't waste the processing time to look for encoded e-mail addresses, but these addresses will still work in a text browser, with screen reading software, etc. Although I still think forms provide the best user experience because they keep the user on site and can be customized to ask the questions you need answers to that users might forget to answer in a freeform e-mail.

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The best way to learn anything, is to question everything.