An image formed by a plane mirror has several distinct characteristics. Firstly, it is always virtual, meaning it cannot be obtained on a screen. Secondly, it is erect, appearing upright like the object. Thirdly, the image is of the same size as the object. Fourthly, it is formed at the same distance behind the mirror as the object is in front of it. Lastly, the image is laterally inverted, meaning the left side of the object appears as the right side in the image, and vice-versa. (Any four of these would suffice for full marks).