Image forming method using registration marks having varying angles

An image forming method having a color alignment system in which a registration mark is printed in each color. Each registration mark has a first line segment extending in a first direction and a second line segment extending from a first end of the first line segment at a predetermined angle with the first direction. The predetermined angles vary among the marks printed. This prevents a complete overlap of two or more marks, thus allowing for sensing and distinguishing of each mark from the others.