If the image is part of the video, then it's not quite bait-and-switch, a as that usually entails substituting something out of the blue; although it may fit Merriam-Webster's definition number 2:
a sales tactic in which a customer is attracted by the advertisement of a low-priced item but is then encouraged to buy a higher-priced one
the ploy of offering a person something desirable to gain favor (as political support) then thwarting expectations with something less desirable
A general term for an enticing image is a teaser.
- an advertising or promotional device intended to arouse interest or curiosity especially in something to follow
MW
So a term for "gaming the preview" would be "showing a teaser" or "doing a bait-and-switch". There may be a more succinct term.