drop shadow image – with right align

I use the well know css solution for wrapping a soft shadow around my images (see above). This works fine for all left aligned images. But in every second posting I want to align the image to the right. So I played a little bit with the code (changed margins -6/6 to 6/-6 and so on), but it doesn’t look nice.

What could I do?

Here the css code for the left aligned pictures:

.img-shadow {
clear: both;
float:left;
background: url(images/shadowAlpha.png) no-repeat bottom right !important;
background: url(images/shadow.gif) no-repeat bottom right;
margin: 20px 0 0 17px !important;
margin: 20px 0 0 8px;
}

.img-shadow img {
display: block;
position: relative;
background-color: #fff;
border: 1px solid #a9a9a9;
margin: -6px 6px 6px -6px;
padding: 4px;
}