I'm sure this has probably already been addressed, but in case anyone else has this issue here is how to work around with one easy cut-and paste:
If you put in a custom header image from merchandising->custom template (you've already copied a shopsite template and edited it etc.), and you insert a standard HTML image map, you might get a blue border around the image.
To get rid of this, go to Edit Template.
In the code of the custom template, the style section probably reads something like:
<style type="text/css">
[-- INCLUDE VAR.ThemeCSS PROCESS --]
</style>
Simply add the following code so it now reads:
<style type="text/css">
[-- INCLUDE VAR.ThemeCSS PROCESS --]
img { border: none; }
</style>
That should fix it.