Final answer:
Chemical fog, base tint, and background radiation can contribute to base-plus fog in photography.
Step-by-step explanation:
The base-plus fog in photography can be contributed to by several factors, including chemical fog, base tint, and background radiation. Chemical fog refers to unwanted fog or haziness caused by chemicals used in the photographic process. Base tint is a color tone added to the base of a photographic print or negative, which can contribute to the appearance of fog. Lastly, background radiation, such as cosmic rays and radioactive elements in the atmosphere and building materials, can also contribute to the base-plus fog.