The idea of allowing compression (or exclusion) based on a file type is used by
other backup products; for instance HARBOR (used to be from New Era I believe)
has a table that can be used to say "DON'T COMPRESS" zip, tiff, etc.

The only challenge might be should this be decision be made strictly by the
client agent, controlled by the server, or under control of the dsm.opt file.

Peter T