Should be able to control it if you put the img class with a max width of what you want. That will (
should) autoscale height as well.
Example from this page:
<img border="0" title="eXpert" src="new_xcart_images/ranks/NX5.gif"/>
The above has no max size defined. If it was bigger, it would appear bigger. The below is constrained to 30 pixels and will scale the height to still be a 1:1 ratio.
<img border="0" title="eXpert" src="new_xcart_images/ranks/NX5.gif" width="30px"/>