I would like to point your attention back to the actual problem.
Thanks to the many details, though.

The initial issue has been to be able to produce BMP BLOBs from EMF
BLOBs "on demand" whenever a client (Crystal Reports) wants to access
the images. EMF has been choosen to save space, so the BMPs should of
course be temporary.
The solution should support any client (including ODBC-based and
IBConsole) so any discussions about API functions helped me to
explain, but not solve the problem.

Anyone has a suggestion for a solution? It seems that UDF+View does
not work (although I still feel that if it doesn't, its a bug in
Interbase, certainly not a feature).
Are BLOB filters the way to go? Will they permit a solution that
doesn't blow the database?

Mirco