'Open and yield file for reading the image file for an image
with supplied identifier.
:param image_id: Image ID'

@contextmanager
def open_for_read(self, image_id):

    path = self.get_image_filepath(image_id)
    with open(path, 'rb') as cache_file:
        (yield cache_file)
    path = self.get_image_filepath(image_id)
    inc_xattr(path, 'hits', 1)
