This plugin is available from WordPress.org, download – WooCommerce Image Hover.
WooCommerce Image Hover is a plugin that is obviously designed to work with WooCommerce. It gives your single product pages a new feature, when you hover over a product thumbnail it will show the thumbnail image as the main image, when you stop hovering over the thumbnail the original image comes back.
Want to code this up yourself? No problem, I wrote a quick how to a while ago called – Product Thumbnail Mouseover Main Image.