From America Needs Fatima:
Among the many miraculous images of the Mother of God through which she deigns to grant her favors, there is one in the monastery church of the Carmelites in Vienna, entitled the Mother of Grace, or Our Lady of Grace, also known as Our Lady of the Bowed Head.
One night while he was praying fervently before the picture, he noticed that some dust had settled on it. Having nothing but his coarse woolen handkerchief, he dusted it with that and apologized, “O pure and holiest Virgin, nothing in the whole world is worthy of touching your holy face, but since I have nothing but this coarse handkerchief, deign to accept my good will.” To his great surprise, the face of the Mother of God appeared to take on life, and smiling sweetly at him, she bowed her head, which thereafter remained inclined.