Center image element in parent div

How I can set center an image element inside a parent div? I would like to do this so that the middle of the image is always in the center of his parent. Also I want the image to always have 100% height (note: I don't want to stretch the image width).

See here for an example: http://jsfiddle.net/Ex5ax/5/

<div class="box">
  <img src='featured.jpg' />
</div>

CSS:

.box { height: 100%; width: 450px; border: 2px solid red; background: green; overflow: hidden; }
.box img { height: 100%; width: auto; text-align: center; }

Add text-align: center; CSS declaration to the parent .box instead of the children .box img.

.box {
    height: 100%;
    width: 450px;
    border: 2px solid red;
    background: green;
    overflow: hidden;
    text-align: center;  /* align center all inline elements */
}

Here is the Fiddle.

Update

It seems there's also a 5px gap under the image, It belongs to the line height reserved characters. To remove that from inline elements like <img> you can use vertical-align: bottom:

.box img {
    height: 100%;
    width: auto;
    vertical-align: bottom; /* <-- fix the vertical gap */
}

JSFiddle Demo #2

You'll need to move the text-align: center; from the CSS for the image to the CSS for its parent div, so your CSS looks like this:

.box {
    height: 100%;
    width: 450px;
    border: 2px solid red;
    background: green;
    overflow: hidden; 
    text-align:center
}

.box img {
    height: 100%;
    width: auto;
}

And that's it!