I was thinking of this technique my mother used to do with mirrors and I just had to try something with it. I emailed her to ask how it was done and she explained the process to me. You use steel wool to sand off the back of the mirror so that the glass shows through. You only do this in the section you want to see through. Then, you place a picture on the back of the mirror. You can really do some ghostly like altered mirrors -maybe something with an old vintage picture. That is what I had in mind but for some reason, I had to do a mermaid first.