I patched PageComment2 from SeungikLee to include captchas (I actually use recaptcha). Thanks to SeungikLee for his great macro, which was easy enough to change.
I only tested the Macro on my 1.5 version, so I would be happy to hear about other versions of moinmoin.
As I am lazy I just link here to my own page for PageComment3. If you want, please transfer the macro here.
In newer Moin versions it can use also TextCha. May be your captchas should be replaced by that. This site has no automated spam since Nov. 2007
As I personally am not a big supporter of TextChas (It takes me usually too long to solve them - just have now to solve: Enter a moin core team member's last name, took me more than 5 minutes to find - I just wanted to offer this for others to have some Choice. Also I have patched 1.5 at other places, so I am a little afraid switching to 1.6. -- UlrichNorbisrath
Current MoinMoin Version is 1.8. btw. TextChas are site dependent. You have to define your own question and answers for your site. I'd never thought that it is difficult to get the name of a core team member. However trusted users never have to answer any textcha question. You can define in your own wiki such a group too, see HelpOnTextChas
If you join us on #moin chat.freenode.net we may be able to help with patching and updating. 
-- ReimarBauer 2008-11-09 18:38:09
Thanks for offering help. I will probably drop in next week. I know, that we are already at 1.8. I think, when I started you had just 1.6. My version is pretty closed down (and might so already violate a little bit the general wiki spirit) and is only used by me and my students (and I expect some friends to comment), but moinmoin still proves to be the perfect product for this. I just thought that this extension might be useful for somebody and wanted to give a little bit back. If it violates any general policies, feel free to remove this entry. Then I will only host it on my site. -- UlrichNorbisrath
everything is fine you are welcome. -- ReimarBauer 2008-11-09 21:09:32