module HexaPDF::ImageLoader::PDF

def self.handles?(file_or_io)

in JPEG format.
Returns +true+ if the given file or IO stream can be handled, ie. if it contains an image

PDF.handles?(io) -> true or false
PDF.handles?(filename) -> true or false
:call-seq: 
def self.handles?(file_or_io)
  if file_or_io.kind_of?(String)
    File.read(file_or_io, 5, mode: 'rb') == MAGIC_FILE_MARKER
  else
    file_or_io.rewind
    file_or_io.read(5) == MAGIC_FILE_MARKER
  end
end