  Intrinsic differences in the processes involved in the development of
electromagnetic and hadronic showers in the atmosphere have been evidenced by
means of a careful analysis of the event image given by the ARGO-YBJ detector.
The images have been analyzed at different length scales and their multifractal
nature has been studied. The use of the multiscale approach together with a
properly designed and trained Artificial Neural Network, allowed us to obtain a
good gamma/hadron discrimination power. If confirmed by further studies on
different event cathegories, this result would allow to nearly double the
detector sensitivity to gamma ray sources.
