def add_header(image_string):

    """
    Adds the base64 encoding header for jpg images
    to a base64 encoded string.

    :param image_string: A base64 encoded image string
    without a header
    :return: A base64 encoded string with a jpg header
    """
    image_string = str(image_string)[2:]
    image_string_with_head = "data:image/jpeg;base64,"+str(image_string)
    return (image_string_with_head)