Add a tag to thumbnail images in albums

Does anyone know how I can add a html tag to the thumbnail images? I need to add this line: <img width="250" height="200" style="filter:alpha(opacity=25)" onmouseover="nereidFade(this,100,40,5)" onmouseout="nereidFade(this,25,40,5)" src="anyimage.jpg" >
This is the code for normal html. The part "style="filter:alpha(opacity=25)" onmouseover="nereidFade(this,100,40,5)" onmouseout="nereidFade(this,25,40,5)" allows me to call a javascript that will add opacity effects. I was wondering if it is possible to add just that part to the thumbnail image tags.

I also need to add this to the header. I'm guessing I need to put it in header.tpl?
<script src="imageopacity.js" language="JavaScript">
</script>

What directory should I put the imageopacity.js file and what should the link be to call it up. Would it be something like "layouts/matrix/imageopacity.js"?

Thanks.

-Andrew