Thanks to American Digest, I found an article by Claude N. Frechette, M.D., "A New Lincoln Image: A Forensic Study," in which Dr. Frechette documents his authentication of an early daguerreotype of Abraham Lincoln.
Believe it or not -- and I believe it after having read Dr. Frechette's article -- the following image is that of Abraham Lincoln in the early 1840s, when he was in his early 30s:
The next image, about which there was no controversy, is that of Lincoln in 1848 at the age of 39:
Finally, we see Lincoln in 1862 at the age of 53: