Christian Effenberger developed Loupe.js, which allows you to add a magnifier to an object on your page. To use it, all you have to do is to download a Javascript file and a small PNG image, and insert the following line of code in the place you want to have the magnifier:

<div><img id="..." onLoad="initLoupe(this.id);" ...></div>

The result is something like this (click here to see it working):