We often hear people cry out about the amount of editing that gets applied to modern images and how photography is now more about the use of Photoshop that the simple truth that was presented in the days of film.
This article from PetaPixel shows how some classic images were developed in the darkroom and shows how dodging and burning are marked up on the test print and then used to emphasize different aspects of the images to produce the final result, techniques which are still in use today using modern post-processing software.
http://petapixel.com/2013/09/12/marked-photographs-show-iconic-prints-edited-darkroom/