...is murky even to the best of us. For homework, you can often "get away" with using images, music, and video by others. But in the real world, you have to get permission (sometimes quite a convoluted process). More information can be found in books about copyright and helpful websites.
Want to use high quality images? Great! ARTstor is here for you...while you're using it for homework.
After you graduate, you have be much more aware of copyright.
For now, though, take advantage of these great images.
Zoom in or capture the whole.
Use Advanced Search or Geography Classifications like I showed you to find the right thing.
David Alan Harvey. "San Miguel." 2005. Vianny. Magnum Photos, ARTstor.