  We derive correlated bounds on ratios of deep inelastic structure functions
from the dipole picture of photon-hadron scattering at high energies. In
particular we consider ratios of the longitudinal structure function, the total
structure function and the charm part of the latter. We also consider ratios of
total structure functions taken at the same energy but at three different
photon virtualities. It is shown that by confronting these bounds with
experimental data we can significantly constrain the range of validity of the
dipole picture.
