1. An image compressing apparatus, comprising: an image reducing section that generates a reduced image by reducing the image size of an input processing target image; a region of interest detecting section that detects a region of interest from the processing target image and generates a region of interest image by extracting the region of interest detected within the processing target image from the processing target image; an image multiplexing section that generates a multiplex image by multiplexing the reduced image and the region of interest image within an image space; and a compressing section that generates compressed image data by compressing the multiplex image generated by the multiplexing section.