Introduction:
A shadow and an image formed by a plane mirror are both visual phenomena that involve the reflection and obstruction of light. However, there are distinct differences between the two.

Shadow:
- A shadow is formed when an object blocks light from a source, creating an area of darkness on a surface behind it.
- Shadows are two-dimensional and lack color and detail, appearing as a silhouette of the object that casts them.
- Shadows are formed due to the absence of light in certain areas, as the object obstructs the path of light rays.
- Shadows change in size and shape depending on the position of the object, the light source, and the surface on which they are projected.
- Shadows do not have a definite boundary, as they gradually fade away from the object's edges.

Image formed by a plane mirror:
- An image formed by a plane mirror occurs when light rays bounce off a mirror and create a reflected image of an object.
- This image is virtual, meaning it cannot be projected onto a screen. It can only be observed by the viewer.
- The image in a plane mirror appears to be as far behind the mirror as the object is in front of it, creating an illusion of depth.
- The image formed by a plane mirror is laterally inverted, meaning it appears reversed from left to right compared to the actual object.
- Unlike a shadow, the image in a mirror is three-dimensional, maintaining the color, detail, and proportions of the object.
- The size of the image in a plane mirror is the same as the size of the object.

Differences:
1. Nature:
- A shadow is a two-dimensional absence of light, while an image formed by a plane mirror is a three-dimensional reflection of light.
2. Formation:
- Shadows are formed when light is obstructed by an object, creating darkness on a surface.
- Images in a plane mirror are formed through the reflection of light rays bouncing off the mirror's surface.
3. Detail and Color:
- Shadows lack detail and color, appearing as a silhouette of the object.
- Images formed by a plane mirror maintain the color, detail, and proportions of the object being reflected.
4. Projection:
- Shadows can be projected onto a surface, while images in a plane mirror are virtual and cannot be projected onto a screen.
5. Inversion:
- Shadows do not exhibit any lateral inversion, while images formed by a plane mirror are laterally inverted.
6. Depth Perception:
- Shadows lack depth perception, while images formed by a plane mirror create an illusion of depth.
7. Size:
- Shadows change in size and shape depending on the position of the object and light source.
- Images formed by a plane mirror have the same size as the object being reflected.

In conclusion, while both shadows and images formed by a plane mirror involve the reflection and obstruction of light, they differ in terms of nature, formation, detail, color, projection, inversion, depth perception, and size. Shadows are two-dimensional, absence of light projections, while images in a plane mirror are three-dimensional reflections of objects.