Posting Confirmation Codes

In my forums I allow guests to post. The problem is before the post goes through they have a confirmation code they have to copy. This confirmation code usually is very hard to decifer whether some of the letters are capitals. If they don't get it correct they lose the post altogether. I'd like to do away with this or simplify it with numerical characters. Can this be altered?

thanks

Can't be done. You can suggest it though with a yes or no poll.