JPEG format, 400x336 pixels, 40% compression, 25 kilobytes

JPEG format, 400x336 pixels, 60% compression, 19 kilobytes

JPEG format, 400x336 pixels, 80% compression, 12 kilobytes

JPEG format, 400x336 pixels, 90% compression, 7 kilobytes

JPEG format, 400x336 pixels, 95% compression, 4 kilobytes

When I look at this particular image, I can begin to see minor degradation at 60-percent compression (most visible on the border of the blue shirt). Eighty-percent and 90-percent compression is progressively worse, and 95-percent compression is badly pixelated. Forty- or 50-percent compression is probably a good value for this image, with an image size of 20 to 25 kilobytes.

Another way to lower the size of the file is to reduce the image size. For example, here's the same image in a 200x168 format:

JPEG format, 200x168 pixels, 40% compression, 12 kilobytes

JPEG format, 200x168 pixels, 60% compression, 9 kilobytes

This smaller image size reduces the file size by a factor of two!

If your scanner is creating 100-kilobyte files, then your scanner is probably producing images in an uncompressed or slightly compressed JPEG format. Using a program like Paint Shop Pro, you can open the image and re-save it at a different compression ratio to shrink the file size significantly.

These links will help you learn more: