In the examples given the Parthenon and the insect are both clear contrast of colour. The Parthenon is lit and contrasts against a very dark sky, possibly night or possibly by increasing the contrast using a NG filter, or digitally. the insect is silhouetted against a light, also probably at night. This could be reversed by having a dark silhouette of the Parthenon against a light blue sky, and in the insect image by having the lights shining on the insect from behind the camera – not into it.
Light and therefore contrast is important in looking at shapes.