Mirror Art is one of those things that are just amazingly awesome and simple to create.
Mirror art is achieved by taking a mirror and placing it next to an existing piece of art. This process can also be duplicated on a computer using digital image editing software such as Adobe Photoshop or a free photoshop alternative GIMP.
There are some examples of mirror art I've created on this site such as this one.
As you can see unique effects can be created using this style of art, including images that look like something else. Some people believe that there are intentionally hidden images within the mirror art and this is especially common with Leonardo Da Vince's works, such as John The Baptist because of the many things he was known for, one was his unique style of writing backwards so you may have to hold his writing to a mirror to read it.
Mirror art is a style that can be applied to many mediums of art and can turn an image that's otherwise uninteresting to most people into something that captures their imagination.