Reverse image search can help you find different variants of the same image by uploading a sample image or retrieving one via URL. Likely the most popular tool to do it could be Google reverse image search via Google Images and its drag and drop feature that allows you to search in Google Images any image that is publicly available in the Internet or uploaded by you. Here you can see other alternatives for reverse image search engines and services that let you find the source of a given image.
This kind of services can be very useful to get the source of any image, for detecting copyright violations but also to find the proper license of an image that you find in the Internet.