simple - images and javascript

Hello. This is, i believe, a really simple question(i'm a newbie).

I'm trying to display an image which, when clicked, would execute a javascript command(in this case, a showOverlay script).

I know how to do this with a simple hyperlink :

<a href="javascript: showOverlay();"> Example</a>

but instead of the word 'Example' i would like to have a clickable image. What is the code to do that ?

 

So instead of Example you would have:

<img src="location of image">