Vertical-align middle with display table-cell not working on images

I'm trying to use the vertical-align: middle on a layout to vertically center sometimes text, sometimes images, but it's only working on text. Can anyone tell me why?

HTML:

<div>
    <img src="http://jsfiddle.net/img/logo.png"/>
</div>

<div>
    <span> text </span>
</div>

CSS:

div{
    width:200px;
    height:200px;
    background-color:red;
    display:table;

    margin:10px;
}
img, span{
    display:table-cell;
    vertical-align:middle;
}

http://jsfiddle.net/9uD8M/ I created a fiddle aswell