In 1977, Alfred A. Blaker, a professional scientific photographer, wrote1:
"...errors do occur, and besides, it is not always possible to make a single exposure that will be optimal for the entire image. I refer to the solution of this problem as differential printing, though this concept is commonly thought of as two separate procedures called dodging and burning in. Dodging consists of interrupting the light between the lens and a small area of the printing paper so as to give less exposure to that area, whereas burning in is the opposite-interrupting the light to the entire paper except for a small area, so as to give more exposure to that area. These procedures are illustrated in Figure 6. [reproduced below]"
Instructions you will not need anymore. But note the sentence I underlined: "When correctly done, differential exposure is not detectable in the final print." Go explain that to the editors of Nature.
In our age of digital photography, however, the established techniques of scientific film photography that were once completely acceptable would get your manuscripts rejected. Item #5 in Nature's new "Provisional guide for digital images":
"Processing (such as changing brightness and contrast) is appropriate only when applied equally across the entire image and when it is applied equally to controls. Contrast should not be adjusted so that data disappear. Excessive manipulations, such as processing to emphasize one region in the image at the expense of others (for example, through the use of a biased choice of threshold settings), is inappropriate, as is emphasizing experimental data relative to the control."
Differential printing, I suppose even if it is applied equally to controls, is now inappropriate.
I recommend that Nature change the title of their guidelines to "Paranoid guide for digital images".
1. Alfred A. Blaker. 1977. Handbook for Scientific Photography. W.H. Freeman.