I would recommend a single HTMl fie per image. This is the template i use for cover pages;
Code:
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<title>Cover</title>
<style type="text/css">@page {padding: 0pt; margin:0pt}</style>
</head>
<body style="padding: 0pt; margin: 0pt">
<div style="text-align:center">
<img style="text-align: center" src="%s" alt="cover" />
</div>
</body>
</html>