a) The image formed by a plane mirror is always virtual, upright, and of the same shape and size as the object it is reflecting.
b) A virtual image is a copy of an object formed at the location from which the light rays appear to come. The main difference between real and virtual images lies in the way in which they are produced. A real image is formed when rays converge and actually meet, whereas a virtual image occurs where rays only appear to diverge.