Photographic prints were re-shot through halftone[0] film (or 'screen') producing a 'screened' version of the image, with dots at various sizes instead of continuous tones. The screened image was then used to expose a sensitized plate, which would be developed to produce a half-toned negative in metal. The high spots took ink and carried it to the paper. More dots, more ink -> darker.

Typical newspapers might use a screen with 80 dots per inch because they are running very fast and using cruddy paper. Art printers on shiny clay paper use much finer screens and get results approaching the original prints.

[0] https://en.wikipedia.org/wiki/Halftone