Opacity setting and image embedding

[jilop]

I love the boxover and keep finding new uses for it. My new idea is to use it for large .gifs with transparent sections in the image. I want these to stay transparent withing the box over. The problem is, when I set the opacity of the box, say 50%, it also makes the image 50%. Is there a way to make the box 50% and the image 100%?