  The components of blazar jets that emit radiation span a factor of $10^{10}$
in scale. The spatial structure of these emitting regions depends on the
observed energy. Photons emitted at different sites cross the lens plane at
different distances from the mass-weighted center of the lens. Thus there are
differences in magnification ratios and time delays between the images of
lensed blazars observed at different energies. When the lens structure and
redshift are known from optical observations, these constraints can elucidate
the structure of the source at high energies. At these energies, current
technology is inadequate to resolve these sources and the observed light curve
is thus the sum of the images. Durations of $\gamma$-ray flares are short
compared with typical time delays; thus both the magnification ratio and the
time delay can be measured for the delayed counterparts. These measurements are
a basis for localizing the emitting region along the jet. To demonstrate the
power of strong gravitational lensing, we build a toy model based on the best
studied and the nearest relativistic jet M87.
