According to the GeoServer documentation for the Image Mosaic extension...
http://docs.geoserver.org/2.4.x/en/user/tutorials/imagemosaic_footprint/imagemosaic_footprint.html
It asks for a shapefile as the footprint data set. Does anyone know if the footprint can be any other type of data set, preferably PostGIS/PostgreSQL or ArcSDE / SQL ?
You should probably look to a database as soon as your mosaic is non-trivial. As user30184 pointed out, there are examples of that.
However Image Mosaic has different levels of capability in different versions of GeoServer.
The documentation page you linked to appears a bit outdated on the supported indexes (even on the 2.6 version of that page), but there is a better explanation on http://docs.geoserver.org/stable/en/user/tutorials/imagemosaic_timeseries/imagemosaic_timeseries.html of how to build the datastore.properties for a PostGIS database. It should be possible to use anything supported by GeoTools JDBC, but I've personally only used PostGIS, and I believe its the main configuration for test / development. Therefore, I recommend PostGIS.
Note that the TimeAttribute (and ElevationAttribute) isn't required unless you actually have time or elevation dependent data and want to expose that through GeoServer. Also, Image Mosaic isn't the only DataStore option for time / elevation data.
Ciao DrStereo, short answer:
ImageMosaic supports footprints as Shapefile or wkb files
More info here
longer answer:
ImageMosaic code can be easily extended to support footprints in raster form or other vector sources. We are planning raster support shortly, other vector sources are unplanned at the moment.
Probably not what you wanted to hear, but life isn't perfect.
Simone.
