title: Get image extension
body: <p>I want get uploaded image extension. </p>
  
  <p>As I know, best way is <code>getimagesize()</code> function.</p>
  
  <p>but this function's mime,  returns <code>image/jpeg</code> when image has <code>.jpg</code> or also <code>.JPEG</code> extension. </p>
  
  <p>How can get exactly extension?</p>