1. Download the Magic Zoom WordPress image plugin.
"/wp-content/plugins/"
/wp-content/plugins/magiczoom/ajax-loader.gif
/wp-content/plugins/magiczoom/MagicZoom.css
/wp-content/plugins/magiczoom/mz-packed.js
/wp-content/plugins/magiczoom.php
2. Activate the plugin in the 'Plugins' menu of WordPress.
3. Add zooming to any image of your WordPress posts by referencing the small and large images. Reference your small image with <img> and link it to your big image using the CSS class of "MagicZoom". Customise it to your satisfaction! Your code will look something like this:
<a href="example_big.jpg" class="MagicZoom"><img src="example_small.jpg"/></a>
Demo: Magic Zoom : JavaScript image zoom tool