There are many compositional techniques that can enhance photographs. “Lines” are one such element and create some kind of mood to the pictures.

There are different kinds of lines that can be used in a picture. If these are used effectively along with the “content”, then the picture becomes stronger.

Horizontal Lines
Vertical Lines
Diagonal Lines
Irregular / combination
Triangle Line. 

Here are some examples of pictures taken with the line as a composition element in various forms.