These online repositories provide high-quality images of artwork and other historically significant items that are in the public domain, so you are free to use them in your papers and presentations, but make sure you cite your source!
You are required to cite images that you insert into essays and visual presentations.
In the body of the essay or in a visual presentation:
More Farmers in Peru Have Stopped Planting Coca, Opting for Cacao and Coffee
Note. From Peruvian Prosperity: From Coca Farmer to Chocolate Maker, by N. Guitierrez, 2016, USAID (https://www.usaid.gov/results-data/success-stories/coca-farmer-chocolate-maker). Copyright 2016 by USAID.
USAID. (2016, September). Peruvian prosperity: From coca farmer to chocolate maker. https://www.usaid.gov/results-data/success-stories/coca-farmer-chocolate-maker
If you refer to information from an image, chart, table or graph, but do not insert it in your essay or presentation, create a citation both in-text and on your Reference list.
If the information is part of another format, for example a book, magazine article, encyclopedia, etc., cite the work it came from.
If you are only making a passing reference to a well known image, you would not have to cite it, e.g. describing someone as having a Mona Lisa smile.