Last few weeks I am receiving lots of spam emails from my jewelry store website. I was considering adding CAPTCHA but than I realized that it is not accessible enough.
I'd definitely discourage the CAPTCHA option as not only are they inaccessible but it'll also be ineffective against most spam now-a-days anyway.
The solution that's worked best for me is to insert an extra question into a form that's compulsory. Something simply like a mathematical problem like "What is 2+1?".
I'd also provide a little bit of text to explain why this needs to be completed.
It's not ideal but has limited the amount of spam on forums and contact forms for me so does seem to work.
validating the value would be simple, you could have 5 math questions that are random, each with a unique number that is passed, when the submission goes to the validation page it can check that uniqe number against the correct math result. If its correct then pass if not send them back.
The alternative to CAPTCHA is called SAPTCHA - this is the technical name for the math question method. Check the extensions for your chosen blogging software to see if anyone has contibuted a SAPTCHA plugin.