Line and shape
Literal lines do not exist in nature, but are the optical phenomena created when objects curve away from the viewer. Nonetheless, line-like shapes are for all intents considered line elements by the artist; for example, telephone and power cables or rigging on boats. Any such elements can be of dramatic use in the composition of the image. Additionally, less obvious lines can be created, intentionally or not, which influence the direction of the viewer’s gaze. These could be the borders of areas of differing color or contrast, or sequences of discrete elements, or the artist may exaggerate or create lines perhaps as part of his style, for this purpose. Many lines without a clear subject point suggest chaos in the image and may conflict with the mood the artist is trying to evoke.

Movement is also a source of line, and blur can also create a reaction. Subject lines by means of illusion contribute to both mood and linear perspective, giving the illusion of depth. Oblique lines convey a sense of movement and angular lines generally convey a sense of dynamism and possibly tension. Lines can also direct attention towards the main subject of picture, or contribute to organization by dividing it into compartments.

The brain often unconsciously reads near continuous lines between different elements and subjects at varying distances.

Straight lines
Straight lines are called linear when used in a piece of art work. Straight lines add affection and can make it look more detailed and challenging. Horizontal, vertical, and angled lines often contribute to creating different moods of a picture. The angle and the relationship to the size of the frame both work to determine the influence the line has on the image. They are also strongly influenced by tone, color, and repetition in relation to the rest of the photograph. Horizontal lines, commonly found in landscape photography, can give the impression of calm, tranquility, and space. An image filled with strong vertical lines tends to have the impression of height, and grandeur. Tightly angled convergent lines give a dynamic, lively, and active effect to the image whereas strongly angled, almost diagonal lines generally produce tension in the image. Viewpoint is very important when dealing with lines particularly in photography, because every different perspective elicits a different response to the photograph. By changing the perspective only by some degrees or some centimetres lines in images can change tremendously and a totally different feeling can be transported.

Curved lines
Curved lines are generally used to create a sense of flow within an image. They are also generally more aesthetically pleasing, as we associate them with soft things. Compared to straight lines, curves provide a greater dynamic influence in a picture.

In photography, curved lines can give gradated shadows when paired with soft-directional lighting, which usually results in a very harmonious line structure within the image.