Probably. But there are some circumstances under which he cannot: (1) If the pictures were taken by you or your husband, or by anyone other than your husband's brother, posting them would constitute copyright infringement. If you or your husband took the photos, you own the copyright in them, and can demand that the photos be taken down on that basis. (2) If the photos are particularly personal, or posted in a context that portrays the child in a false light, your state's privacy laws may provide a basis for demanding that the photos be taken down. (3) If the posted photos are used in a commercial context, then the use of your child's image without permission violates the Washington State Personality Rights Act, which prohibits commercial (usually advertising) uses of a person's name or likeness without permission. If none of the above scenarios fit the situation, then the brother's posting probably does not violate any law or give rise to a basis for a civil action.