Hi, welcome to the forums--
How comfortable are you with Advanced Actions? I have an idea of how I'd tackle this, but it involves executing some Advanced Actions to show images (like a check mark) upon the success and failure of the questions. It would also involve showing custom feedback captions instead of the default ones, since the default captions pause the slide and any images in an Advanced Action would show /after/ clicking the slide to continue.
Have you checked out Lilybiri's blog? I don't remember if she has any articles about this particular scenario, but she does a lot with custom questions and Advanced Actions: http://blog.lilybiri.com/