Down-sample the factors of resolution by 2 for each dimension.
For example - ,Reduce the 640 x 480 resolution to 320 x 240 resolution.

Code the smaller image with another JPEG mode.
Decode the image and up the sample encoded image.
Encode the difference between the decoded image and the original image.
The above process can be repeated for multiple times.
This process provides high quality images with low resolution display.   _{Your Comment}