Many online stores offer potential buyers the choice to view large version of images of products, but increasingly there is a tendancy to allow 'zooming' in on products to see more detail. Amazon allows this with many of its products, for instance.
There is a plugin for jQuery which does something similar (ish) which I've add to my store demo. Click on the product name for one of the products, I suggest the iPad or iPod Nano, to view this in action. In the overlay window, hover over the image and you will see how this works. Well this nifty little plugin is called jqZoom, but I also found a non-open source alternative that doesn't use jQuery called Magiczoom, which is used on a number of commercial sites.
You will notice that a few of the images are missing from the demo. With jqZoom, you need to store small and large versions of each product image, although the large image only gets loaded when you hover over the small image. Each image is stored as a Blob linked to the product. As I was loading up the images using the application I kept getting a 'ORA-01691: unable to extend lob segment.....' error, so I need to look into this.