Every other browser is rendering this correctly.
<body>
<div>
<div><img src="img/logo_top.png" width="168" height="85" alt="Logo top" /></div>
<div><img src="img/logo_bottom.png" width="168" height="83" alt="Logo bottom" /></div>
</div>
</body>
It's the same thing without the divs, and with a < br /> between images.
Update:
Here is my HTML, with doctype:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" >
<head>
<title>Test</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<style type="text/css">
img {border: none;}
body {font-size: 0px;}
</style>
</head>
<body>
<div>
<div><img src="img/logo_top.png" alt="Logo top" /></div>
<div><img src="img/logo_bottom.png" alt="Logo bottom" /></div>
</div>
</body>
</html>