I've searched google, your forum's search, the only spam protection I could find was suitable for 1.4.x, what about 1.5.x guys? :)
I have an akismet API key, which is entered in the appropriate box in "comment settings" in "gallery configuration".
I'm sure the experts on here can help you better than I can if you are unsure what I mean.
Try this section of the docs - http://documentation.coppermine-gallery.net/en/comments.htm#comments_options_spam
Where can I download http://documentation.coppermine-gallery.net/en/configuration.htm#admin_comment_captcha_start this one?
Please try reading the docs I linked to. They will tell you how to enable the features that are built into the package ::)