So far, I\'ve tried a bunch of things to the effect of the following, without success:
I got here because I was looking for a solution to fading background images based on a option change. I combined what I had already written with Hussein's jsfiddle above and came up with this jsfiddle.net/v4BMC/.
This initially stacks two identical images on top of each other. When the is changed, the top image's style attribute is removed, the bottom image's src is changed and the top image is faded out to reveal the bottom one. (The top image finishes with a style="display:none" which needs to be removed at the beginning of the operation, otherwise it doesn't work.)
Hope this is useful to someone else and not too irrelevant to be included here!