Dimension Independent Centred Images - This allows an image to be centered within a parent container of a fixed height no matter what height or width the child image is. http://jsfiddle.net/jamessouth/JpCXX/

centered-image.css

/*
 * 1: Arbitrary width.
 */
.parent {
    position: relative;
    height: 250px;
    max-width: 400px; /* 1 */
    overflow: hidden;
}

/*
 * Position the image absolutely and then move it's four positions
 * 1000000% out of the container. This with an auto margin is the core of the trick.
 * Why such a large number? Firefox seems to have issue when using larger images even
 * at 100%.
 */
.parent img {
    position: absolute;
    top: -1000000%;
    right: -1000000%;
    bottom: -1000000%;
    left: -1000000%;
    margin: auto;
    max-width: 100%;
}