Finally I figured out how to kill the spam - without having to use word verification. All I did was go into my dashboard in Blogger and click Settings. Then click Posts and Comments. You will find a question "Who can comment?". I changed from anyone to Registered User - and that doesn't let anonymous comments through. Don't forget to click on the orange Save Settings button towards the top right or else nothing will change.
I was a bit worried that some legit comments would be stopped - so I changed my little spiel about comments to ask anyone who had trouble to email me - but all the normal comments seem to be coming through just fine.
So if the thing stopping you killing the "prove you are not a robot" thing is the spam - I think this might solve your problem. And it really is in your blog's best interests to change to no word verification - it does put so many people off from commenting on your blog.