You currently have this in your stylesheet...
Code:
a img { border: medium none; }
You could replace that none with a color code and see how you like it. However, without more specificity, that would affect all images on the site that happen to be links -- probably not what you want.
But if I were me I'd put a border on images in my image editing program. I'd prefer the control I have there over shades and colors. I used to have a faint shadow on the right and bottom of my images for the same reason you want a border, but that wouldn't work on a black site.
Rob
PS
I was having fun trying to work out what an iron hose man would sell.