The use of images for teaching and scholarly research generally falls under the category of "fair use." The terms of fair use states that, in an educational context, the payment of fees or permission is not required from copyright owners.
For more information, the Visual Resources Association (VRA) has published a Statement on Fair Use of Images for Teaching, Research, and Study. This statement is a guideline and should not be considered a legal document.
There are different rules for publishing images. If you are using images for publication, you must determine if they are in the public domain, or are protected by copyright.
The Visual Resources Association have also developed a Digital Image Rights Computator (DIRC) to help users assess the intellectural property status of a particular image so they can make informed decisions about the intended educational use of an image.
Images, diagrams and artistic works should be cited as any other type of work. Give as much information as possible about the image used, including these basics:
creator's name (author, artist, photographer etc.)
date the work was published or created
title of the work
place of publication
type of material (for photographs, charts, online images)
website address and access date
name of the institution or museum where the work is located (for artworks and museum exhibits)
dimensions of the work (for artworks)
Ship in a Storm, by Henri Rousseau, Circa 1896, oil on canvas, 1844-1910, 54x65 cm.
The Ship in the Storm by Henri Rousseau
Credit: Peter Willi