Right after World War II returning southern Blacks realized it was time to stop existing in state of fear. Many, after being overseas during the war became fully cognizant of just how horrible the repressive segregated South was and began departing "Dixie" by the hundreds of thousands, while others started demanding their rights as American citizens, like voting.
The Klan countered in many respects and reverted to the Civil War banner being that it represented slavery to them and they flown the Rebel flag ever since. Resulting from Klan ideologies of hate being identical with neo-Nazis, when today's hate rallies are staged each grouping of depraved thugs always displays their favourite banners.
The other relevant point was to demonstrate the swamp rats Klan members of today do not run around with the American flags (unless desecrated!) but are promoters of a new "old South" as the photo documentation clearly depicts.