Answers:
1. General Grant seems to have put on a lot of weight. That's because the body used in the photo actually belongs to Major General Alexander McCook.
2. The head is taken from a photo of the general outside his tent at Cold Harbor.
3.A nd what is supposed to be City Point in the background is actually a photo of Confederate prisoners captured at Fisher's Hill.
Source: 10 truly weird mysteries of the civil war.
bonus: Answer.
David Acheson Company C, 140th Pennsylvania Volunteer Infantry.
Source.
https://www.gettysburgdaily.com/the...-states-avenue-to-the-wheatfield-road-part-3/
Edit - After reviewing all the answers that were given, I've decided that the following ten items can be considered problems with the picture in the main question.
1. Anything to do with Grant's head.
2. Anything to do with the fact that the body on the horse wasn't Grant's.
3. Anything to do with the fact that the horse wasn't Grant's
4. Anything to do with the fact that the background wasn't City Point.
5. The fact that the number of stars on the uniform didn't match Grant's rank.
6. The fact that the shadows on Grant don't match the shadows on the tents.
7. The fact that Grant didn't carry a sword.
8. The fact that the horse is "floating in the air."
9. The fact that the soldiers are not looking at Grant while he is supposedly addressing them.
10. The fact that the soldiers are seated with the general in the immediate vicinity.
hoosier