comarison of N images

I have N nummber of images say n1,n2,n3,n4,n5,n6 stored in one folder i want to compare like this and stored all o/p in one location n1 and n2 -o/p1 n2 and n3 -o/p2 n3 and n4 -o/p3 n4 and n5 -o/p4 n5 and n6 -o/p5 so on help me out thnx