Image related features.
The purpose of this extension is to extend the browser's media (mostly image) handling capabilities.
There are plenty of settings which can be customized, and reviewing them is currently the best way to learn about what the extension is capable of.
Sections on the options page, and their brief explanation:
Enriches the built-in photo viewer with different customization possibilities (different sizing modes, custom background/border, hidden scrollbars, etc.) and functionality (zooming with mouse wheel, larger image detection, image rotation, etc.).
▪ Hover zoom
Loads images (or HTML5 video/audio, or albums of these) inside a pop-up on the current page by hovering the mouse cursor over their links/thumbnails.
Global features (like shared shortcuts, which work both in Viewer and Hz), or other features with less options.
An expandable set of rules for getting the larger image, media or other content.
It has more than 200 rules by default, which support thousands of sites across the web, including the popular ones such as Reddit/Imgur, Wikipedia (or any WikiMedia based site), deviantART, Google services (Images, YouTube, G+, Picasa...), Facebook, Twitter, Flickr...
Image bookmarking with thumbnails. It's intended to store only the image address (plus sources) without the need to save the image locally or push it to the cloud. It has a simple tagging/searching system.
List of user defined rules for dis/allowing specific sites.