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JPG image size is dependent on the original image size and the amount of compression given to the data. The image dimensions and colour depth obviously have a large impact on the file size but if the file can be compressed heavily then it will give a smaller file size. Images that contain large contigous blocks of similar colours usually compress very well but images with lots of fine detail and strong contrasting colours do not :) So, yes - it is possible to have a highly compressed 1024x768 pixel image that is smaller on disk than an almost raw 640x480 pixel image :D