Given the short nose, camouflage and US markings it can only be one of 10 aircraft.
YB-24A serial 40-702 delivered May 1941 which spent its life at the USAAF Ferrying Command Training School; or
B-24A serial numbers 40-2369 to 40-2377 delivered 16 June to 10 July 1941, which again went to Ferrying Command (with 3 later going to Consairways for runs to the South Pacific from April 1942)
AIUI the large US flag markings on nose and upper fuselage date the photo to pre-Pearl Harbor for aircraft flying overseas, so probably the photo is of one of the B-24As. These aircraft carried RAF style camouflage as built.
"Two B-24As (40-2373 and 40-2374) were used to transport the Harriman Mission to Moscow in September of 1941 via the United Kingdom. The last leg of the flight to Moscow involved a nonstop distance of 3150 miles, and from Moscow one of the USAAC B-24As continued on around the globe via the Middle East, India, Singapore, Darwin, Port Moresby, Wake Island, Hawaii, and back to Washington. The other B-24A returned to the USA via Cairo, Africa, the South Atlantic, and Brazil."
Some individual aircraft history here (the last 40-2377 seems to be missing)
The rest of the YB-24 and B-24A built were delivered to the RAF in 1941, in lieu of later long nosed LB-30 from the French order.