Design a View that lets folks pan and zoom images. Include + / - button, a hand button, and react to clicks, drags, and scroll wheel actions.
The best way to do this is likely to use the webdev module, and have Java resize the image inside the webdev endpoint script based on the zoom level. After the resize, a pan might be able to move the x y coordinates of the image in a coordinate container, which would be faster than hitting the endpoint again, as long as the image wasn't too large.
It would also be useful to have a "Loading..." message, in case folks use this with really big images, as image resizes for large images aren't always instantaneous.