A quick analysis of file size versus JPEG quality

For a sample genuine photo - http://upload.wikimedia.org/wikipedia/commons/0/0b/ReceiptSwiss.jpg - with all its analog goodness, I just used Paint.Net to resize the photo to 972x1296 and to produce:

Quality(%)   FileSize PNG          2MB 100%         749KB 95%          239KB 90%          153KB 75%          84KB 50%          57KB 25%          41KB

Pictures and more at http://slodge.com/photocompression/