For class use, there are no restrictions on appropriation of images. You can download and use any images you find on the internet in your assignments.
- This does not, OF COURSE, mean you can hand in someone else’s work as your own. You can, however, use any photo as part of a montage. Do not use someone else’s manipulated photo. Start with raw material and make it your own.
Outside of assignments, there are laws that govern the use of other people’s images. If you are making art for publication, any art that is not specifically labeled FREE needs to be licensed. The gray area is: how much of an image can you use or use in a manipulated fashion before you need permission, usually paid permission.
The government has posted some guidelines.
Eileen MacAvery Kane has a very interesting blog that covers this and many other ethical/legal issues related to digital art and to working as a freelance or full-time artist. Ethics in Graphic Design