two possibilities. Most likely it is the result of a grease filled die, buy when I was a kid we would rub a section of the coin with an eraser for a long time until the area disappeared.
Hi there, unfortunately, the lift source you used is hovering directly over the date, making it impossible for us to give you a good answer. If you can retake the photo and not use flash and/or use a light that is not sorting directly above the coin, but north of it, it will be really helpful. Also, please try to take straight on shots of the coin, with the camera parallel to the coin and move the camera a little closer, as long as it doesn’t get blurry (see if you have a macro setting). @ldhair