Email verification? Email verification is no filter!
If you use an activation email, there really isn't a need for a captcha. Captchas are useful because users don't need to leave the current website, check their email, activate it, and come back -- they would have lost their thought inertia at that point, assuming they arrived at the verification step because they wanted to do something useful with whatever application.
If I am missing the point, do explain; I fail to see something to consider to add from that picture. That captcha is also terribly breakable.
To clarify, that was a popup to subscribe for email delivery of an RSS feed via Feedburner. I suppose they put the CAPTCHA in place in hopes of lowering the ability to abuse that feature for flooding.
