When storing images a lossless format (png seems the best option for us) is
often advisable. However to keep load times down it is often advisable to
convert images to a lossy format for display.
mediawiki doesn't seem to offer this cabability atm (if im wrong please close
this bug report pelease point me to the right place).
i propose a simple extention to the image syntax just allow a section to be the
desired format (identified by its standard 3 letter extention). IE
[[image:bighiggqualityphoto.png|thumb|500px|jpg|this is a photo of something