In theory: Backlight is a photographic technique in which the camera is pointing directly toward a source of light. This effects usually hides details, causes a stronger contrast between light and dark, creates silhouettes and emphasizes lines and shapes. The Sun, or other light source, is often seen as either a bright spot or as a strong glare behind the subject.

Please, read Definition of Nature in Rules. Very carefully.

Some people believe that the unique purpose of photography, as compared to other visual arts, is to capture this fleeting, quintessential, and holistic instant in the flow of life. For this reason, many photographers often mention the decisive moment, or similar ideas about capturing the essence of a transitory moment, when they describe their work.

Completely free topic, no restrictions. Let imagination be your guide.

Originally developed to model the physical world, geometry has applications in almost all sciences, and also in art, architecture, and other activities that are related to graphics. It is concerned with properties of space that are related with distance, shape, size, and relative position of figures. Feel free to use imagination and every element for making elements of geometry.

Please, see rules. PSA and FIAP has slightly different definition for this rule.