An Image is a picture which is displayed in a Picture box, is all - any other controls you add to the PictureBox.Controls collection aren't actually drawn on the Image at all, they are drawn on the screen (or other Graphics context used to displaying the PictureBox) but do not in any way, shape, or form alter the Image property.
If you want to modify the Image, your have to get a graphics context for it, and draw onto that.
But ... if you want to take a "snapshot" of the picturebox complete with Image and controls on top of it, look at ethe
Graphics.CopyFromScreen Method (System.Drawing) | Microsoft Docs[
^] - it should let you do that onto a new bitmap, which you can do what you like with afterwards.