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. I'll probably remove that part of the comment stuff soon.
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.