If someone uses a visual work without permission or a license granted by the image owner or copyright holder, it is considered copyright infringement. What is Copyright Infringement, aka Image Theft? Still, official registration of your copyright can put you in a better position if you end up taking someone to court for serious image theft. That means that technically you don't have to register your work for it to be copyrighted.

Copyright for a photo exists from the moment a work is created - in the case of a photograph, from the moment you snap the picture. To begin, you may wonder if it is necessary to register your copyright first to obtain it. That is why the best thing you can do as a photographer is to learn how to find your stolen images online with smart monitoring, believe it, they're out there. Unfortunately, online image theft is common, and if you, as an image owner or creator, don´t think it could happen to you, you risk losing potential income and recognition. The internet allows photographers, illustrators, and other visual artists to display their work online.

Google advanced reverse image search