"Uncle Josh at the Moving Picture Show" was a derivative imitation, or remake, of the English film "The Countryman and the Cinematograph" (1901), the latter of which was made by Robert W. Paul. Edwin S. Porter and the Edison Manufacturing Company likely would've simply duped Paul's film, which they did with other European pictures, if it hadn't featured a cinematograph projecting the films, as opposed to "The Edison Projecting Kinetoscope". Thus, "Uncle John at the Moving Picture Show" provided the company, which also manufactured and sold projectors in addition to films, an opportunity for advertisement. At least in what survives of it now, Paul's film doesn't feature title cards, while Porter's film goes to some length to describe its product and films-within-the-film. The films-within-the-film include a title card each, including one for "The Black Diamond Express", which was a subject made a couple times for the company and which probably had to be filmed again, from a longer distance, for this film. Reportedly, the dancing-girl film, "Parisian Dancer" was from the Edison subject "Parisian Dance" (1897), although every filmmaker made numerous dance films back then.
The entire plot and optical effects of matte shots and optical reduction follow what Paul had already accomplished. Country rube climbs on stage to dance with dancing-girl film - he runs away from approaching train film - he tears down screen after seeing himself in third film, revealing the projectionist - punitive ending. The title cards, which are an early example of such, seem to be Porter's only original contribution to the subject (back then, magic lantern slides usually served to introduce a film's title at exhibitions). At least since Paul's film is now missing some footage, this remake shows us what's missing.