Here is what I use
div.illustration {
margin: 0 0 0 0.5em; padding: 0;
border: 1px solid black;
width: 50%;
float: right;
}
div.illustration img {
border: 0; margin: 0; padding: 0;
width: 100%;
display: inline;
}
div.illustration p {
margin: 0; padding: 0;
text-align: center;
text-indent: 0; font-size: smaller;
} /* With thanks to Elizabeth Castro */
<div class="illustration">
<img src="images/source.png"
alt="alt text"/>
<p>caption</p>
</div>
It is modified from Elizabeth Castro's excellent book
EPUB straight to the Point. Although it's written mainly for the iPad it has lot's of good stuff. I also like her book
HTML, XHTML and CSS
Regards, Alex