The Art Connoisseur is a contract in Mission 3 of Dishonored Death of the Outsider.
The Art Connoisseur Walkthrough
This contract is so easy, I actually got it by accident. Right next to the skiff near Dead Man’s Bluff, a new barge will appear during Mission 3. There is a locked cargo area on the barge that contains one of the paintings you need for the Art Aficionado trophy. Luckily the key is so close by, its almost ridiculous. Dive in the water, look under the barge and you will see a corpse floating underneath it. Loot the corpse to get the key, open the door to the cargo area and grab the painting to complete the contract.
All Mission 3 Contracts: