Need help with mouseover images

Ugh. Can someone please take a look at the following page and offer some insight as to why I am getting a small black line below my mouseover images?

http://www.kentonfriendsofyouth.org/skyjuice/home.htm

My script has no reference that I can tell of that would cause this. Has anyone experienced this issue before?

Thanks in advance for any help you may be able to offer!

EDIT: By the way, here is the text from the external .js file I'm referencing:

img0_on = new Image();
img0_on.src="images/button_bandinfo_ON.gif";
img1_on = new Image();
img1_on.src="images/button_showschedule_ON.gif";
img2_on = new Image();
img2_on.src="images/button_links_ON.gif";
img3_on = new Image();
img3_on.src="images/button_audiovisual_ON.gif";
img4_on = new Image();
img4_on.src="images/button_email_ON.gif";

img0_off = new Image();
img0_off.src="images/button_bandinfo_OFF.gif";
img1_off = new Image();
img1_off.src="images/button_showschedule_OFF.gif";
img2_off = new Image();
img2_off.src="images/button_links_OFF.gif";
img3_off = new Image();
img3_off.src="images/button_audiovisual_OFF.gif";
img4_off = new Image();
img4_off.src="images/button_email_OFF.gif";

function over_image(parm_name)
{
document[parm_name].src = eval(parm_name + "_on.src");
}
function off_image(parm_name)
{
document[parm_name].src = eval(parm_name + "_off.src");
}

Thanks!