From the moment the dying Lincoln entered the Peterson House late Friday evening until he expired and his body was removed from the house shortly after his death the next morning, I can assure you
there was not a single minute that there were less than at least 8 or 10 people in the Lincoln bedroom. Having said that, it was virtually impossible without Stanton's approval and under his direction that a photo could be taken at all. As none of the numerous witnesses in the bedroom ever revealed in conversation or writing that a Lincoln photo was taken, it can be stated without a doubt that if a Lincoln death photo exists, the photo was not taken in the Petersen House.
Photos in the Petersen House WERE taken in the morning right after Lincoln's body was removed from the house. The Ulke Bros., professional photographers, were living in the house at the time and are assumed to be the originators of two photos of the bedroom including the empty bloodstained Lincoln bed. These two rare photos are today well known.
So is it possible a undiscovered Lincoln-in-death photo still exists? Yes. If so, it most probably would have been taken covertly during the time when Lincoln's body was transported by train back to Illinois for burial. The journey made many stops at larger cities where the body was displayed. In New York City on April 24th one such photo of Lincoln in his coffin was secretly taken. The photo was undiscovered for nearly 100 years before surfacing in a library in Albany. There could be more somewhere. And if so, such a photo would logically have been taken from a distance, not close-up as Lincoln was heavily guarded as he lie-in-state.