Not an ASP (Application Service Provider) application.
No recurring costs, free updates.
Stepless Zoom, Pan and Crop interface with mousewheel support.
Various image protection options.
Source images and tiles never load into cache!
No plugins like Flash, Java or Silverlight required.
Compatible with all major browsers.
Skinable over CSS and more than 300 customizing parameters.
Branding free. Any image and text can be replaced.
Native PHP GDlib and ImageMagick support.
Build in galleries: vertical, horizontal and "inline", all with a slideshow option.
Single source imaging - on-the-fly generation of all necessary thumbnails and tiles.
Batch conversion with a single php file - can easyly be integrated into any CMS.
Many different ways of integration!
Several API methods.
Integrateable with popular "lightbox clones" that support Ajax content or Iframes.
iPad / iPhone support.