anchor: love.image.isCompressed
  Determines whether a file can be loaded as CompressedImageData.
  compressed = love.image.isCompressed( filename )
  filename string The filename of the potentially compressed image file.
  compressed boolean Whether the file can be loaded as CompressedImageData or not.
  compressed = love.image.isCompressed( fileData )
  fileData FileData A FileData potentially containing a compressed image.
  compressed boolean Whether the FileData can be loaded as CompressedImageData or not.