  In this paper, we demonstrate that CME-driven shocks can be detected in white
light coronagraph images and in which properties such as the density
compression ratio and shock direction can be measured. Also, their propagation
direction can be deduced via simple modeling. We focused on CMEs during the
ascending phase of solar cycle 23 when the large-scale morphology of the corona
was simple. We selected events which were good candidates to drive a shock due
to their high speeds (V>1500 km/s). The final list includes 15 CMEs. For each
event, we calibrated the LASCO data, constructed excess mass images and
searched for indications of faint and relatively sharp fronts ahead of the
bright CME front. We found such signatures in 86% (13/15) of the events and
measured the upstream/downstream densities to estimate the shock strength. Our
values are in agreement with theoretical expectations and show good
correlations with the CME kinetic energy and momentum. Finally, we used a
simple forward modeling technique to estimate the 3D shape and orientation of
the white light shock features. We found excellent agreement with the observed
density profiles and the locations of the CME source regions. Our results
strongly suggest that the observed brightness enhancements result from density
enhancements due to a bow-shock structure driven by the CME.
