How to prevent the user from accessing the image/video by just putting the filename in url

Hi ! I m developing a community site where user can upload photos/videos and share with his friends. I am saving the images and videos on server.How can I prevent the user from accessing the image/video by just putting the filename in url ex:www.test.com/userdata/fdfdfdfd-dfdfdfdfd-dfdfdwerer.jpg have to check whether the user has rights to see the content or not
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