Add a CATCHA to a ASP.NET Website

I'm looking for a freelancer to add a CAPTCHA code to my ASP.NET website and validate if it's completed or not before proceeding. The desired CAPTCHA type to use is an image CAPTCHA. I'd like potential freelancers to include their experience in applying for this job. As far as backward compatibility goes, I'm not sure if it will need to be supported, so this should be taken into consideration when completing the project.