I don’t know much about geometry but I do know an aesthetically pleasing photograph when I see one.
In fact most of us can, and the reason is geometry, or more precisely the geometric shapes such as squares, triangles, circles and lines that make up patterns that form the image.
Our brains are hardwired to see patterns in all sort of ways not just in photographs but in our everyday lives in the events that happen around us. It could be that our ability to recognise patterns in the real world kept us alive when we were hunters and, sometimes, the hunted. Learning to recognise that the sound of the bushes rustling was often followed by a large predatory beast looking for its lunch helped keep early humans alive.
Patterns also appear in data, and being able to recognise those patterns can help us solve a problem with the data. Once we have broken it down into individual patterns it makes it easier to solve, and quicker to do so next time.
Patterns also help us make sense of the world, bringing order out of chaos. Without patterns there would be anarchy. Of course there are occasions when we see patterns even if they don’t exist. It is attempts to make sense out of random events that can lead to conspiracy theories.
When we come to photographs patterns are the building blocks; they can be shapes, textures, shadows. They can create a sense of balance or rhythm through reptition or symmetry. Alternatively, breaking the pattern up can create tension in the photograph.
Here are a few examples of my own work which in different ways display examples of patterns.
Shapes

This photograph of a wooden fence is made up of a series of shapes, circles, rectangles, a hexagon and a horseshoe(!)
It is also worth pointing out that in this, and in all the other images below, there is an extra shape; the square or rectangular border of the image itself. When thinking about shapes, it’s worth considering that as part of the composition.
Circles

A very obvious shape is a circle such as this shadow of a garden table. Interestingly we cannot actually see the entire circle because it is broken by the leg of the chair. Our minds however still perceive the complete circle, making up the messing part. The chair adds a degree of interest to the photograph, breaking up the shape. It would be a very much less interesting photograph if it were just the circle.
Lines

Patterns work well when they are repeated such as in the black lines of these railings in the foreground. A repetitive pattern can be a bit boring, though. Adding a contrasting element can make it a bit more interesting. In this example the softer shape of the plant, creates a juxtaposition between its more amorphous structure and the strong lines of the fence.
Shadows

We can see patterns in many forms and different types of photographs. In this example of street photography the shadows cause a striking pattern but you also have the bench and the drain cover in the foreground, creating a wide range of geometric shapes across the picture.