When it comes to citing text from someone else's work, the rule is to provide a proper citation and source. Once you do that, you're off the hook. But when it comes to copying images it seems to be more complicated. There are copyright rules, and I read online that you always need to contact the author before using images. But if I provide a proper source for the images I copy, why should it be any different from citing text (which is fine)? Furthermore, it is not always possible to contact the author for permission of use; for example, what am I to do if the author is not alive anymore (say I want to copy images from a book published in the 1930s)?
So I need some guidance here, what is really permitted when copying images from books and other sources?