Image compression results

[Florent]

You're right, it's pretty good! But maybe I should rephrase my question:

How WebPageTest can make such an assessment (ie, state that a gain of 40% is achievable as well known tools as jpegtrans, imagemagick can not even win one byte)?

It should be based on some specific tool/library that would be very interesting to know in order to try to achieve the above result (unless WebPageTest use JPEGMini? ).