When several items have the same style you give them a class name, and make a css statement for that class.
<p><img src="images/colorbar.gif" class="my_images" alt="colorbar gif" /><p />
On the style sheet:
Because it's a style statement the height is given in pixels, not just a number.
It's interesting that you can just style a div as a line separator too, to replace an image or an HR.