Several times I’ve run into the situation where I have moved an AbleCommerce store and CAPTCHA is broken.   Login page works fine, it just doesn’t show the CAPTCHA image.
The problem (at least in my situation) was when I’m moving these sites, I’m updating them from ASP.Net 2.0 to 4.0.   To do this, I use the appropriate web.config file from the /Install/Framework/ folder provided by AbleCommerce.
The only problem is the replacement web.config does not include the appropriate HTTP Handlers to drive the CAPTCHA control in AbleCommerce.
The solution is simple.   Directly above the <httpModules> section in the web.config, add:
And now the CAPTCHA will work again in AbleCommerce.