@MrTIMarshal Yes, of course, you could substitute your images - although they're not as nice as mine
. Depending on the size of the images you'll probably need to adjust the css as well - so that the span sits neatly with the checkbox.
For browsers < IE9 we would have to reinstate the opacity of the checkbox and remove the background images from the span.. or try and push it behind the checkbox (bleugh!!).