As much as possible, Trivium Art History uses images of artworks and writings that are in the public domain. Works in the public domain are those whose intellectual property rights have expired, have been forfeited, or are inapplicable. Artworks and writings enter the public domain when their copyright expires. Determining when a work's copyright expires is complex, but in general a work is in the public domain in the U.S. when it was created before 1923, and in most countries when the artist/author has been dead for 70 years. For these works, unlimited copy, distribution, modification, and reuse are allowed for free.
For a more detailed breakdown of when works enter the Public Domain in which countries, we use Peter Hirtle's chart: Copyright Term and the Public Domain in the United States — 1 January 2015 from the Cornell Copyright Information Center.
Occasionally, to provide a more complete and accurate understanding of art history, for scholarship and education, we will use copyrighted materials, which fall into two cases: images from museums's and institutions who have relseased images of their collections into the public domain via "Open Access" programs, and work whose copyrights still stand but we use under the bounds of educational fair use.