Put the width and height in separate attributes, with no unit:
<img style="margin: 0; border: 0; padding: 0; display: block;"
src="images/img.jpg" width="120" height="150">
Another Option:
<!--[if gte mso 9]>
<style type="text/css">
img.header { width: 600px; } /* or something like that */
</style>
<![endif]-->