Very Large Image manipulation

[magick]

ImageMagick can handle terabyte image files. To make it fast you could first convert the original image to the MPC format. MPC images are memory mapped with near zero overhead. To pan, zoom, or crop from the Web use the MagickWand for PHP or IMagick PHP wrapper. There is a book called Pragmatic Ajax that discusses how Google maps uses AJAX to manipulate large images. That may be a good start.