1. An interactive method of transmitting detailed image data to a user over a communications channel extending between a transmitting station and a receiving station, comprising the steps of: transmitting a user request for image data to the transmitting station; obtaining a digitized image data set in a computing device at the transmitting station, said image data set defining an image with a spatial resolution; performing a lossy compression operation on the digitized image data set, using the transmitting station computing device, to produce a lossy compressed image data set; storing the lossy compressed image data set at the transmitting station; transmitting the lossy compressed image data set to a computing device at the receiving station with the same said spatial resolution as the digitized image data set; decompressing the lossy compressed image data set at the receiving station, using the receiving station computing device, to produce a lossy decompressed image data set; displaying the lossy decompressed image data set on a display device visible to the user at the receiving station, in the form of an image having the said spatial resolution; providing an input device permitting the user at the receiving station to select at least one window of interest within the displayed image data set; monitoring the input device to receive a user selection of the window of interest and transmitting information defining the window of interest to the transmitting station; transmitting, from the transmitting station to the receiving station, additional image data pertaining exclusively to the image within said window of interest, but inhibiting the performance of this step until the user interactively requests an accurate reproduction of the original image data in the currently selected window of interest; using said additional image data received at the receiving station after the user requests an accurate reproduction of the original image data in the currently selected window of interest, enhancing the displayed image within the window of interest to produce a display within the window of interest which accurately reproduces the original digitized image data set, while maintaining the same said spatial resolution in the window of interest.