I'm trying to add a very simple gallery where the photo is at the top and thumbnails are underneath. All I want to happen is that the photo changes when you click on one of the thumbnails. I've been trying to search for this but the galleries all seem to have stuff I don't want.

I tried the following and it does change the image but it also opens up the thumbnail.

Code:
<img id="im" src="photos/039.jpg">
<a href="photos/t001.jpg" onclick="document.getElementById('im').src='photos/001.jpg'"><img src="photos/t001.jpg"></a>