http://jsfiddle.net/xJmZt/
As you can see in the above example , there is extra height of about 6px on the div.
div
That extra height is gone if line-h
Images by default are defined as inline elements so they follow text rules, you can either set the container height to match the images', or give the image display: block or vertical-align: bottom.
display: block
vertical-align: bottom