Get specified letter as image
        :param pixelletter_id: ID of the letter
        :return: JPG-Letter-Unicode-String if successful else None

def get_letter_as_image(self, pixelletter_id):
        """
        Get specified letter as image
        :param pixelletter_id: ID of the letter
        :return: JPG-Letter-Unicode-String if successful else None
        """
        image_letter = self._make_get_request('letters/previews/{}_1.jpg'.format(pixelletter_id))

        if image_letter:
            return image_letter

        return None