Burke and HareGoofs
When the photographer takes the picture of the cadaver in Doctor Robert Knox's premises, he removes the glass plate from the camera and exposes it to (low level) light in the room. That action would have spoiled the photograph and an image is visible on the photographic plate. This would not have been seen.
Two hangings are shown in the film, in the style of a "long drop" designed to break the neck and cause instant death. This style was first introduced in the 1870's by William Marwood as a more humane approach. Before then, and certainly in 1828-1829 when the film was set, the victim was simply suspended by a rope around the neck, and choked to death by suffocation.