flushing the cache for just one image?

You might find a way to do this, although it's not worth the effort. I've found that browsers can be reasonably intelligent about using their cache. One way to 'fool' them into updating is use a different filename for the image, then--as long as the browser gets the new version of your page--it will use the new image.

The file name would be something like: heart02.jpg, or heartnew.jpg Hope this helps.

I wonder if this would work:

<img src="filename.jpg?r=<?= time() ?>" with="50" height="50" alt="etc" />'

I used something similar to prevent caching of a dynamically generated css file once and it worked a treat...

<? time(); ?> is a php function...

If you want to use Javascript you will need to make a function that will either create a random number and attach it to the end of the image, or create an array that will randomly select one to show.