This was a design concept/pattern that I first saw in use for an interactive on a website to show the before and after images of a natural disaster event.
Since then I have seen it pop up in a couple of different places, but mostly used to show before/after images in an interactive side-by-side comparison. Below is an example that I saw on a website showing the transformation of one type of image into another.
Would this UI component be classified as a slider, an image interaction or something else?
This is the only implementation of the design pattern that I have seen (with the slider in the middle of the overlaid images) but if there are sightings of alternate designs please also add them to the answers.