Here's the Family Knowledge Answer 1...
Ok.. so your mother says it's your brother who gets the picture you both want. IF you have a FNQ lesser than that of a piece of concrete, which by the way never talks and so has not that bad a FNQ, you cut dead all you believe have insulted you which includes bad mouthing them.
If your FNQ is cosi cosa, you accept the decision, but not really, and in your heart you harbor resentment toward both your brother and your mother and anyone else who sides with them. This makes for awkward silences at family barbecues and the occasional nasty crack that comes out of nowhere, but not really.
Here's the deal. RULE OF FAMILY #1 is that you can never get in between someone and their mother. Which means that your mother and brother have their own thing between them, and very possibly he has paid for the picture in ways you have not, and probably don't care to. You just don't know. So you keep the gracious heart and let it go. Your mother however may have broken Rule #1, since she got in between you and herself unless she had good reasons, which she could have.
There is something to keep in mind...you are under no obligation to be a doormat,so when it turns out that the picture is A. stolen property, B. worth quite a bit, so it means the government is taking a huge bite out in taxes, or C. Radioactive so it's making people who own it sick, you are under NO obligation whatsoever to post bail, contribute any money to the Feds, or pay hospital bills for your brother and his family who must take radiation therapy for ten years.