I added a presentation on Slideshare which I use to introduce the notion of 'planning poker'. It uses Doggy Planning to practice with the deck.Furthermore, it contains some CC licensed images from Flickr.
I use this presentation to show why relative estimates are important. For the doggy planning, I allow some discussion as to 'what on earth are we estimating here', and in the end end up with some metric to estimate. I only show the image of the dogs after the 'right questions' have been asked (e.g., "what kind of poodle is this?"). If you have any ideas to use this better, please let me know!