1. An image compression apparatus, comprising: an image reducing unit for reducing an input image having a first resolution at a predetermined reduction ratio to generate a reduced image having a second resolution lower than the first resolution; a reduced image compression unit for compressing the reduced image to generate reduced image data; a reduced image expansion unit for expanding the reduced image data; a region of interest setting unit for setting a region of interest corresponding to a predetermined target object in the input image; a high resolution conversion unit for converting a partial image of an area of the expanded reduced image corresponding to the region of interest to a partial image having the first resolution by applying a prediction process that uses a learning result obtained by learning the predetermined object in advance; a differential image generation unit for generating a differential image by taking a difference between the partial image converted to the first resolution and a partial image of the region of interest portion of the input image; a differential image encoding unit for encoding the differential image to generate differential image data; and an output unit for outputting the reduced image data and the differential image data.