There are many plugins which zooms the images. Image Zoomer exactly comes under those category. This is a small file of 3.7 kb which utilise the jQuery zoom tool. The plugin have the ability to be magnified any image when the mouse rolls over it, see a snapshot of a Image Zoomer enabled photo.
Small file size and easy to upload and activate the plugin.
Simple customization. The default zoom level is 2x and The default size of the “magnifier” is 75×75 can also be changed.
When the user scrolls the mouse wheel while over the image, the zoom level decreases or increases based on the scroll direction. The range of zoom can be changed from 1x to 10x.
See the demo of the plugin from the plugin homepage here and download the plugin from wordpress plugin directory here.