Image swap



Image swap refers to the rare event when a post's attached image is erroneously replaced by the attached image of an unrelated post. Sometimes only the thumbnail is swapped, other times a "full swap" swaps the true, expanded images entirely. Sometimes there is no swap, one simply overwrites the other. Image swaps seem to happen when images are processed at the same time in the eyes of 4chan's servers.

4chan servers index images by a 13-digit UNIX timestamp which has the precision of a millisecond, which makes collisions not too hard given you roll the dice enough times. As of 2021, image swaps are not too infrequent on boards like /pol/, /v/ and /vg/, which peak at 150 posts per minute on a daily basis.

The rarity of the phenomenon makes it hard to study. Conclusions shouldn't be drawn from archives, as they often do their own processing, which may change the nature of the image swap, or may even fix it.

Theoretically, an image swap can happen not just with two images but three, four, five... Although I couldn't find any instances of a triple swap or quadruple (but I didn't search either). Of course the already minuscule chance of two images colliding at the same exact millisecond exponentially diminishes with each increment. But it shouldn't be impossible. = Further reading =
 * Instances of image swaps are often reported at the time's respective general thread for meta discussion (if it is alive):

= Notes =