Old photograph that was painted with something

Old photograph of man and woman that was went back over with chalk like stuff. It is very old   Found in my great uncles attic when he died. He brought it with him from jasper,Al. He must have  known them. My dad seen the pic before in alabama about 40 years ago. The frame is also very old. Took it to local people the could not tell me anything on it but the wanted to buy it