Reverse image search takes a picture as the query instead of words and returns pages where that picture, or a close variant, has appeared. The practical value is not the search itself but the timeline it exposes. If the earliest indexed appearance is years old and shows the same scene with a different caption, the current post is recycled. If the earliest appearance is a stock photo, a film still, or a game render, the origin is settled. If the earliest appearance is the post you are already looking at, the image has no independent history — which is informative but not conclusive, because a genuinely new photo can also have no history.
Video search works the same way through keyframes: extract a distinctive frame, search it, and look for the same footage under a different label. The interpretation rules are identical, and so are the failure modes. Reverse search misses images that are new, private, heavily cropped, mirrored, or recolored, and it returns nothing for a scene that was never posted anywhere else. A null result means "no earlier copy found," not "no earlier copy exists."
The simulation below lets you run this workflow on a sample and watch how the earliest-match date and the caption history change your reading of the same picture.