Picture Frame That Opens Like A Door

I have some lovely postcards that my sister sent to me and I would love to frame them in such a way that the front side with the art/image is displayed on a wall, but the frame has a little knob so that I can be opened to read the message on the back of the postcard if I wanted to without having to take the frame off the wall or taking the backing off the frame - essentially I could just leave the post card in the frame on a wall and have the ability to pull a little knob to open the picture frame like a little door to read the other side. Thanks in advance!