title: Best security way to allow image profile by external url
body: <p>Suppose that I have a web application where users can attach a link in their profile to show the avatar (displayed after with img tag).</p>
  
  <p>This is safe? I think it is not.</p>
  
  <p>What is the best way to check if the url provided is a real image? There are other solutions?
  (for now I don't want any upload).</p>