Given the decorative corners on the frame, I perceived it to be an empty picture frame.
Ah. And. In the walking frame, there is one for... *gets confused for a moment thinking he saw something proving frame* Okay. In the walking frame, the object in question has speckles on the inside, so is not likely to be an empty picture frame as there are no speckles in the same general area around it. There are also two body lines, and the rear arm, which is holding the front of the object in question, is also doubled, while the front arm, which is holding the rear, and wrapping its hand around to the front further forward of the body, is missing.
Mirror it is. :)
Which completely changes the comic for me. Thanks for asking!