short subject vs picture show

short subject and picture show both are nouns.

Word	Noun	Adjective	Verb	Adverb
short subject	Yes	No	No	No
picture show	Yes	No	No	No

As nouns, picture show is a hypernym of short subject; that is, picture show is a word with a broader meaning than short subject:

short subject: a brief film; often shown prior to showing the feature
picture show: a form of entertainment that enacts a story by sound and a sequence of images giving the illusion of continuous movement

short subject (noun)	picture show (noun)
a brief film; often shown prior to showing the feature	a form of entertainment that enacts a story by sound and a sequence of images giving the illusion of continuous movement