You'll have 100% control of the image border like this:
Code:
<img src="path/to/image/here.jpg" style="border: 2px solid #f00" />
The first value sets the border width, the second sets the style (solid, dashed, grove, etc.) while the third one sets the color.
Note: If you don't want a border at all just replace it with "border: 0".