PHP or Javascript code for something that changes the image size. If you find such code, then determine why it executes when you first load the page but not when using the back button. In the PHP code use:
<?php echo "Test - this code executed"; ?>
Then you can see if and when it runs.

In the javascript use: alert("javascript executed here;

So now you know about your javascript.

If you still can't find the problem then it is either HTML or CSS.

You need a really good layout program like Dreamweaver to clean up your HTML code. I gave up on Front Page and Interdev years ago because they were nightmares for maintaining table structures. But anyway your problem could be from using % for column widths.