What Is Going On Here?

an optical illusion or trick photography?

Mark Blank-Settle of the BBC found that two of his toddler's train track pieces appeared to be different until he placed one on top of another, so what is happening here? it's something called the Jastrow Illusion, in Jastrow’s words: 'in judging areas, we cannot avoid taking into account the lengths of the lines by which the areas are limited, a contrast in the lengths of these is carried over to the comparison of the areas.' basically we’re measuring the outer arc of the bottom piece against the inner arc of the top piece, in our minds, we make a judgement on the size by simply comparing the inner arc length to the outer arc length, however the outer arc (on both pieces) will always be longer than the inner, if the tracks are moved to a more “appropriate” place, either on top of each other or not aligned at their edges, you won’t inadvertently make comparisons between the inner and outer arcs and you’ll realize they’re actually the same size, what a neat illusion.