The highest resolution file that I could find for the Mona Lisa is this one below from wikipedia (link to wikipedia image). In the interest of keeping this page as compact as possible the one below is reduced to 271 kbytes:
I pieced that file together to form the image below.
Keep in mind that the image in the center is reversed.
This close up of Exhibit A is a mirrored image of the object seen near Mona Lisa's right arm (left side from your perspective):
The same image as above turned upside down:
A final look at Exhibit A as constructed from the retouched image found at wikipedia:
And on to Exhibit B:
And Exhibit B as constructed from the retouched image found at wikipedia:
When you take the three image composite shown earlier and mirror that image from the bottom there is yet more imagery revealed:
Closeup of Exhibit C:
To see these things for yourself I suggest finding the largest resolutions copies of the Mona Lisa that you can. Get several variations from various sources. You will need a decent graphics editor that lets you zoom a few thousand percent. These files are large, so you will need a decently equipped machine as well.
So what are these things? I do not know for sure, but it looks like witchcraft to me.