  The hypothesis that the QCD vacuum can be modeled as a dual superconductor is
a powerful tool to describe the distribution of the color field generated by a
quark-antiquark static pair and, as such, can provide useful clues for the
understanding of confinement. In this work we investigate, by lattice Monte
Carlo simulations of the $SU(3)$ pure gauge theory and of (2+1)-flavor QCD with
physical mass settings, some properties of the chromoelectric flux tube at zero
temperature and their dependence on the physical distance between the static
sources. We draw some conclusions about the validity domain of the dual
superconductor picture.
