In pics you can only capture what a camera lens sees. A moderately skilled naked eye can discern between nickel and stainless by color/tone. Other obvious signs are the "S" stamps on the barrel and cylinder bushing on stainless pieces. The dead give away is the front sight pins, nickel pythons always came from the factory with nickel pins; stainless steel examples always came with blued pins.I attempted to capture what is obvious to the naked eye. Top is a late production stainless 6" bottom is a mid 1960's 4"