The likeness of an object carried and formed by light in a mirror is called an image. For example, your image is a reflection of your face in the mirror. An image can be seen in the mirror because the light reflected from an object falls on the mirror and it is reflected. So, light incident on any smooth shiny surface like a mirror bounces back into the same medium. This bouncing of light by any smooth surface is called reflection of light. Mirrors change the direction of light incident on them. The image in a plane mirror is the same size and colour as that of the object. Moreover, the distance between the image and the mirror, is the same as the distance between the mirror and the object.
When an opaque object blocks the path of light, a shadow is formed. A shadow is a black dark outline. Its length changes with a change in the position of the source of light. Shadows can be seen only on a surface or a screen.
A glass that acts as a mirror on one side and plain glass on the other is called a two-way mirror. A two-way mirror is used when you want to observe people without letting them know that they are being watched, for example, by police or in psychological institutions.
Images formed by a pinhole camera are entirely different from the images that are formed by a mirror. The image formed by a pinhole camera is inverted and smaller in size when compared to the object. The image is also not clear. Moreover, the distance between the object and the pinhole is not the same as the distance between the pinhole and the image.
A periscope is an instrument used for observing objects from a hidden position. This instrument is mostly used in submarines, and works on the concept of reflection in plane mirrors. Using mirrors, it enables people in a submarine to view objects on the surface of the water.