Alfred Hitchock enjoyed appearing in his own films in brief cameos, as an early easter egg for fans. Watching a Hitchcock film, part of the fun is trying to spot Hitch. In this supercut, Morgan T. Rhys has found those cameos and assembled them into an easy-to-follow video.
This is a rare case in which using the desktop YouTube interface, with its "annotations," is actually useful, because Rhys draws a YouTube box around Hitchcock whenever he appears. On platforms that don't show the boxes (meaning, most mobile devices), you may have to rewind a bit to find him in some of the shorter scenes.
My favorite cameo is from Lifeboat, shown around 1:56. How do you add a walk-on part to a film that occurs entirely in a lifeboat? The master of suspense figured out a way.
(Via Dangerous Minds, which includes a list of the films and their release years.)