How to tell if a painting is old or a reproduction

[0x0DizzYx0]

thank you very much for your information I own a little antique shop in Coeur d'Alene Id. and just received about 20 old paintings. I am trying to find artist and value very difficult. I have several that the back looks like the one in your vedio. If you could offer up any advise it would be greatly appericated.. Thank you. Something Special Cd'A Id.

[vardanyan20]

i have an old painting that only has last name of Hoffman. it also says in the back "hecho en mexico" also has "royal #541". could you please tel me if this is antique or not.