I created the base image in Sketchbook Pro- but have more image control in photoshop- so I dressed him there. I took some generic Creed-like boxing shorts and cut them in half and placed both halves on different layers and used warp under Edit>Transform>Warp to mold the shorts to make them appear to wrap around the mannequin. In order to make the arm in the foreground seem to overlap- I simply erased part of the top layer shorts image- and that's it- digital pantaloons
ciao
