I've manipulated images myself during my wet darkroom days, both during the film development process, by using the temperature of my fingers, and easier (because it's easier to see what's happening) by dodging and burning during the exposure of the print and again using my fingers.
Ah yes, the finger 'trick'.
Trick because in my first trimester in photography school,
everything had to be shot 4x5, B&W and all prints made had to be 'straight' with zero dogging and burning. The idea in those very old days was, we students needed to learn to properly expose and light and no print manipulation was allowed. Contact proofs on the back of the print board had to be supplied so the instructor could verify we didn't dodge and burn the 8x10 print itself. We fudged this all a tad using the wet finger trick; it did work unless we went overboard and the sharper instructor's would catch us. Then the mounted print would come back from critique with "Remake" on it. We had to start from scratch with the entire assignment.
It was a tough lesson and a tough first trimester but we learned to expose and light with little regard to darkroom manipulating.
Of course this was a good decade before anyone had any idea what Photoshop would or could be.....