It is probably something so obvious that I cannot see it . The first image does not center, yet the second does. What am I missing?
<body>
<div style="text-align: center; width: 100%;">
<div style="width: 900px; text-align: center; vertical-align: middle;">
<img style="width: 900px; height: 84px;" alt="Header image" src="images/site_header.jpg">
</div>
<div style="text-align: center; vertical-align: middle;">
<img style="width: 900px; height: 49px;" alt="Header sub-image" src="images/nav_back.jpg">
</div>
</div>
</body>