Did Curtis remove all signs of 20th century life from his photographs?

No. Many critics point to a single photographs in which an alarm clock was removed from a photo, but in that same image Yellow Kidney (on the left) wears pants made from a modern woolen blanket. It's possible that he had the clock removed simply because it was visually distracting. There are many signs of modern life throughout The North American Indian, including Natives wearning Euro-Western dress, living in Western-style wooden houses, and using Western implements.

How much money did Curtis make from The North American Indian?

The North American Indian project cost the current-day equiavlent of approximately $25 million to complete, but Curtis worked without a salary for most of the 30 years it took to complete the work.

Did Curtis have a trunk full of costumes that he used for his portraits of people?

No. According to two of his children who traveled with him after they became young adults, they never saw him use any regalia or objects that weren't offered by the people he photographed. It's true that some regalia appears in his photographs mutliple times or, more rarely, clothing from a particular Native Culture appeared on people from a different culture. It is thought that these were presented by the people Curtis photographed.

Why don't any of Curtis's portraits show people smiling?

Curtis was photographing using a large format view camera. This style of camera, which is still used today, employed a film holder that would be inserted at the back of the camera once the subject was set and focus made. The film, however, used by Curtis was a glass plate negative. The glass plate negatives in Curtis's time were produced by Eastman Kodak and had a film speed of ASA 14. Most modern day sheet or roll film used today has a film speed of at least ASA (ISO) of 100 and often more. The result of using this type of film, and all photographers of Curtis's time were using this or something very similar, was that the exposure time was fairly long. Compared to todays film speed, whether it be your digital cell phone or other digital camera was that it was not possible to simply point and shoot as the film was too slow. Often to help hold people steady during long exposures the photographer would use a head brace placed behind the subject such that it didn't show in the portrait. This head brace gave the subject something to lean into and would help steady them for exposures of 3 or more seconds. The issue with smiling is the facial muscles can't hold steady for that long without some twitching which would render the mouth area a blurry mess. This is why we see and relate to old photos as being very ridged and stoic.

Why do old black and white photographs show native peoples so dark?

This is the result of the type of film used of which there are two types of black and white film, Orthochromatic film and Panchromatic. In a nutshell, orthochromatic film is what was used until the late 1920s by most all photographers, panchromatic is what is used today and considered a modern type film. The difference in the two films for this discussion is their light sensitivity. Orthochromatic film is sensitive mostly to the blue end of the light spectrum and not sensitive to red wavelengths. The result is anything photographed with red, or hues of red, don't record well or at all rendering them as very dark when printed. One benefit of using this type of film emulsion is a red safelight maybe used in the dark room for loading the film and for processing the film as well. Panchromatic film is sensitive to a much wider light spectrum and renders things of red in a more acceptable way, but the film must be loaded and processed in total darkness. With the popularity of tintype photography these days, you may have noticed people with blue eyes photograph very strikingly as the eyes print almost white. Where as people with dark skin, red hue, photograph very dark. For a more detailed explanation see here: https://filmphotographyproject.com/content/howto/2018/07/panchromatic-orthochromatic-film/