Set the poster or thumbnail of a this Vidoe.

def set_image(self, image, filename=None, resize=False):
        """
        Set the poster or thumbnail of a this Vidoe.
        """
        if self.id:
            data = self.connection.post('add_image', filename,
                video_id=self.id, image=image.to_dict(), resize=resize)
            if data:
                self.image = Image(data=data)