Interesting situation. Most of the time folks WANT hotspots hidden as they often detract from the image.
I might think the simplest solution would involve just editing the image so the desired indication is there.
But if you are determined to work with code to accomplish it, the link below may provide some clues.
Thanks for the tip, Rick! That's an interesting article. May have to give it a try.
Actually, my description wasn't really clear. I want the hotspots to be invisible until the user touches one with the mouse pointer. I'm after a "hover" effect that makes the hotspot visible temporarily to alert the user that it's there. I have placed an instruction right above the image map telling the user that parts of the image can be clicked to view descriptions.
Okay... Are you by chance using the Technical Communication Suite?
If so, Adobe Captivate would be the easiest way to accomplish this. That's the approach I would be taking. I'd create what I like to call a "one slide wonder" that has all the rollovers in it. The plop the Captivate right onto the page.