It looks like from DANFS entry, that this photo could date from roughly mid-June 1941.
Only a short time before, on 15 June 1941, Task Force (TF) 3, commanded by Rear Adm. Jonas H. Ingram, had inaugurated patrol operations from the Brazilian ports of Recife and Bahia; resources available to Ingram included Omaha and three of her sister ships, and five destroyers. Her propulsion and engineering issues resolved, Omaha stood out on 30 June to conduct Neutrality Patrols between Recife and Ascension Island, British Overseas Territory. It was Omaha’s duty, as part of Ingram’s force, to intercept, board, and inspect vessels to enforce a blockade against German trade in the region. She also served as a convoy escort to protect the shipping lanes between South America and West Africa. During that period she made port calls to Montevideo, Uruguay, as well as Bahia and Rio de Janeiro, Brazil. She operated under war conditions.
On 4 November 1941, the British oiler Olwen reported a German surface raider attack at 03°04'N, 22°42'W, prompting Vice Adm. Algernon U. Willis, RN, Commander-in-Chief, South Atlantic, to order the heavy cruiser HMS Dorsetshire (accompanied by the armed merchant cruiser HMS Canton) to investigate. Light cruiser HMS Dunedin and special service vessels HMS Queen Emma and Princess Beatrix were ordered to depart Freetown, Sierra Leone, to join in the search.
Dorsetshire and Canton then parted company, with the former steaming southeast and the latter heading toward a position to the northwest, the Royal Navy ships to be supported by TG 3.6, Omaha and destroyer Somers (DD-381), which were at that time well to the northwest of the reported position. Memphis (CL-13) and the destroyers Davis (DD-395) and Jouett (DD-396), near to the location given by Olwen, searched the area without result, while Omaha and Somers search unsuccessfully for survivors. The next day [5 November], the search for the “German raider” reported by Olwen continued, with Vice Adm. Willis informing his ships of the unsuccessful efforts by the five U.S. ships (two light cruisers and three destroyers) that had been involved in the efforts the previous day