The diverging rays emanating from every point on the facing surface of an object facing a plane mirror forms a virtual image in the back of the mirror at the same vertical distance as it is in front of the mirror following the laws of reflection and we get a similar impression of the facing surface of the object as a virtual image in the mirror. So the face of image just faces the face of the object both havimg same size. This phenomenon appears to us as there occurs a lateral inversion. As the object and image face each other right side of the object forms left side of the image and vice versa but top and bottom of the object form image at top and bottom respectively . So no vertical inversion occurs.