Social media users have a contract with the platform from the moment they started their accounts. Images uploaded afterwards are ruled by said contract.
Like any other image, they are protected by copyright, even when they are not registered, therefore anyone that considers republishing the image, must inform where it came from.
Even if we run into the images by chance, somebody took them, their author, we cannot assume the is no author. If they use the image without authorization, they may face legal consequences.
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