I'm using ristretto 0.8.0-1 (The highest version which can be chosen in this deprecated(?) bugtracker is 0.3.3).

For some reasons unknown there are still image files floating around with extension e.g. '.png', although the file contains a jpeg image. When trying to open such a file ristretto gives the error:

   Fatal error reading PNG image file: Not a PNG file

and displays nothing. Interestingly the thumbnail preview to the left inside ristretto doesn't care and displays thumbnails of such files.

What I expected is behavior like in

  XnViewMP: No problem, it doesn't care about file name extensions and just uses the magic byte to determine the file type and displays it
  IrfanView: Also uses magic byte, but gives a warning and asks if the file should be renamed automatically. Clicking on 'yes' will simply change .png to .jpg for the above example