just fyi, my gallery got spammed last night.
some 500 entries, manually (I don't think a bot could read the captchas and the entry time varies) but with changing IP-address.
So this wouldn't be helpful.
I'm going to disable the comments for a while.
i just did some reading on bots overcoming captchas.
this is an issue but in my case I think/guess it was done by a human (telling from the patterns in my log).
I increased the number of captcha characters to 7 which makes it a bit harder to read and fitted some extra words into the simple spam filter.
I hope this lasts for a while.