It was once proposed to do an automated search of images from the
Clementine probe for evidence of lunar lava tubes. The argument (by
Taylor and Gibbs) was that the usually-cited candidates for lava tubes
are the huge, apparently partly collapsed rilles visible from Earth or
in Apollo photos and that any tubes at these sites may be too deep to
use easily. The thought was that smaller tubes could be just as
useful (for radiation and meteoroid protection), more numerous,
possibly located near more interesting sites, and easier to access.
These smaller tubes might be discernable in some of the 1.9 million
Clementine images.

Did anything ever come of this? If not, did anyone ever begin a
_manual_ search of the 620,000 high-resolution visible-light
Clementine images? This sounds about right for a small NASA grant or
for a volunteer, distributed project among interested space cadets.