1991 DDO Obverse.oponions Please.

Just machine damage after the strike. On the bust, you will see this on the area next to the edge of the bust near the fields.

On hub doubling the doubling appears further in on the bust outline. (note the image on the left)
On machine damage you will see it at the outside edge of the bust. (note image on the right)
On the ear that is also MD. Note how it reduces the size of the normal devices. If it were hub doubled, then the ear would be enlarged. Just common classic MD. Keep looking.

Note on the first image below how the dub doubling makes the area to the right of the spread as tapered. (showing light to dark)

If it were MD, that area would all be the same color like the image on the right of the half dollar that shows MD.

Another view of hub doubling near the mouth area:

Note again the contour color (light to dark) on the left side of the hub doubling. Again note on the half dollar image of the right, the same color (because there is no contour in that area because it is flat because of the MD)

Here is a side by side of the last image and MD cent.

Note the outer area of the bust is affected by Machine Doubling. (only color because of flat shelf like damage after the strike.

So if were have hub doubling (a doubled die) on the bust, it will not be on the outside edge of the device. It is inside a bit and shows a contour between the spread and the edge of the bust. On MD it is flattened at the outside edge of the bust. Hope this helps.