SQL & PL/SQL :: DBMS_CRYPTO Hash A BLOB In A Union Over Dblink?

With this table in local and remote database via a DBLink

CREATE TABLE PICTURES (
ID NUMBER(12),
PICNAME VARCHAR2(20),
PICTURE BLOB
);

How come I can get the hash of the picture column fine like this:

SELECT dbms_crypto.hash@dbLink(PICTURE, 3)from SCHEMA1.PICTURES@dbLink;

but I can't do it in a union with the local database?

SELECT dbms_crypto.hash@dbLink(PICTURE, 3)from SCHEMA1.PICTURES@dbLink
UNION
SELECT dbms_crypto.hash(PICTURE, 3)FROM SCHEMA1.PICTURES;

gives "ORA-06553: PLS-564: lob arguments are not permitted in calls to remote server"