I had a small scale problem with this, and it's been fixed in 1.4.2 - you'll see when you upgrade there... It shows the IP address of the sender on the message receipt.
Custom image captcha which worked well for about 6 months until two weeks ago. We're seeing about two spammer signups a day now and we're going to have to change the pictures and questions to see if that stops the bogus sign ups.
Not certain how the solvemedia captcha is setup - that looks interesting.