USA - unusual cancel on picture postcard. Apparently sent by a French tourist the stamp has been placed - in the European style - on the picture side of the card.
The regular machine postmark of BROOKLYN NY STA C DEC 6 1911 is applied to the address side, though inverted.
The 2c red Washington definitive is cancelled (but not tied) with 25 in a circle or oval, and the date 6-12-11 added alongside.
The initials alongside the date are those of the sender of the card.
Trinity Building, N Y City, published by Roth U. Langley N.Y.