I too thought 300 dpi was large, but I read (somewhere) that that's desirable for ebooks. I will research further.
Each image is in a div like this:
<p><img src="a.luciano.jpg" alt="luciano on tram" /></p>
<p class="caption">At work on the tram: Luciano (top) and his three partners. Victim’s cap is visible at lower left.</p>