Look at the blocking of the shading in the shadows. I try to use JPG quality 5 or higher for scans I want to show on the web.

Here is an interesting site that shows the results of using higher and higher compression ratios for a jpeg image. You need JAVA on your pc to see this:

http://micro.magnet.fsu.edu/primer/java/digitalimaging/processing/jpegcompression/

Look at the blocking as you get beyond a compression ratio of about 15.