<<Nevertheless - do you agree with my statement that blob-filters can
only be (actively) used with embedded sql, and not, for example,
Delphi components that access Firebird?>>

Missed that :-) The answer is yes and no :-)

The problem relates simply to the following..... you either have to write the
blob handling code at the api level (using the relevant api calls that support
the filter from/to capability) or use the embedded SQL statement

e.g.
INSERT Blob Blob1 INTO TABLE1
FILTER FROM -1 TO -2;

Nothing like this is supported at the DSQL layer.

Regards
Paul