title: How can I know the format of a UIImage? (IOS)
body: <p>Very simple question.</p>
  
  <p>Is there any way to tell whether a picture picked from the photo library is a jpg file or a png file?</p>
  
  <p>Since some other app's work may also be in the library, so I need to know this.</p>
  
  <p>More specifically, what I need is only to tell whether that photo is a JPEG image.</p>
  
  <p>Thanks !</p>