One of the welcome new features in "BetterHTMLExport" is the ability to generate a navigation bar on the picture pages. It's great for moving from page to page, but there's no link to return back to the thumbnail page, which is a real problem.
However, you're also allowed to include text from iPhoto's "Comments" field to accompany the image on the picture page. If you add a little HTML in the Comments field, such as:
<br />Return to the <a href="../index.html"> Classroom Thumbnails</a> page.
you can generate a text link that appears on the picture page and will take your viewer back to the thumbnails page.