Formal Elements
The formal elements of photography are what make up a photograph: line, shape, pattern, texture, tone, focus.
Lines can be horizontal, vertical, diagonal, straight, curved. There can be many lines, and there can be one.

Shape does not only tell us what the object is; it also tells us how big or small or heavy or light it is. This can be done with relationships with other objects. For shape to be the main focus, it needs to stand out. Other elements cannot clutter the frame, otherwise attention will be drawn to those.

Pattern is lines, shapes, textures, and/or colors organized in a rhythmic way. Iteration is a pattern with shapes that repeat to some degree. They fill the frame and become a texture. Pattern perception depends on scale. You can emphasize patterns or break them. By emphasizing patterns, you no longer focus on the individual objects, but rather as a whole.

Texture is a 3D version of pattern. Patterns enhance sense of reality and add visual interest, especially if irregular. Texture can be enhanced by different types of lighting.

Value is the range of light and dark. Tone is a color mixture that is not a pure color hue.

Focus is what the camera captures in most detail, what is blurry and what is sharpest in detail.

I don’t think its possible for an image to only have one element at one time. Even if you had a white wall, white is value, and the wall has texture, whether it is smooth or rough. In order for there to be a line or shape there must be contrast with the background and therein lies value. You can’t isolate any element by itself; there will always be at least one other element.