A reverse image search is a search engine function that takes an image file as input and returns results related to that image, such as other websites where it has been used. This can be useful for finding the original source of an image, or for finding similar images.
Reverse image search engines typically use image recognition algorithms to match incoming images with images in their database. Google's reverse image search is one of the most popular, but there are also dedicated reverse image search engines such as TinEye and Image Raider.
To perform a reverse image search, the user simply needs to upload an image or provide a URL for an online image. The search engine will then return results related to that image.