A morgue file originally was the paper-folders containing old files and notes that were kept by criminal investigators, and old article clippings kept by newspaper reporters, in case they became of later use as a quick-reference.
In modern usage, its scope has expanded to cover many post-production materials for use of reference, or an inactive job file. The term is popular in the newspaper business to describe the file that holds past issues flats. The term has also been used by illustrators, comic book artists, designers and teachers.
The newspaper magnate William Randolph Hearst forbid his papers from keeping a morgue file on him.
Artist Doug Wildey was known for his huge morgue file of photo references. He became so adept at depicting actual people, that it becomes an ancillary enjoyment trying to identify the celebrities' cameo appearances in his artwork.