Hi,
Instead of linking directly to the large picture:
<a href="images/PictureLarge.jpg" ><img src="images/PictureSmall"/></a>
perhaps you could link another xhtml page containing the large image:
<a href="PictureLarge.xhtml"><img src="images/PictureSmall"/></a>
Then PictureLarge.xhtml would be something like:
..
<body>
<img src="images/PictureLarge.jpg" width="100%"/>
</body>
..