Power Thumbnail enables you to generate thumbnails with the existing attachment system. It offers two kind of thumbnails.
Basic Resizer — make thumbnails with given width or height.
Advanced Zoomer — split large images into small pieces and load them like Google Maps (you can drag, move and zoom the picture). The loading speed is faster when you apply Advanced Zoomer to large pictures.
Here is a DEMO
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Free Download: Download this wp-plugin