In your fist example:

<img height="100" src="/forums/uploads/3865.jpg" width="100" align="center" border="0" />

You can move an image to the left or right on the Web page or control its vertical placement with the ALIGN property, but you can't center it using the ALIGN attribute. align="center" isn't valid HTML. All browsers ignore align="center" when it's part of an IMG tag.

---

<div align="center">&#160;<img height="100" src="/forums/uploads/3865.jpg" width="100" border="0" />

 

In the second solution you enclose the image inside a DIV element that CAN be aligned to the center.

 

Hope it helps.