Assume that most works you want to use are copyrighted and you need permission to use them.
Check for clear copyright statements, or terms of use.
You do not need to seek permission if …
- The material is not or cannot be copyrighted
- You merely link to it
- The material is in the Public Domain
- The material clearly states that re-use is permitted or it is openly licensed through Creative Commons (ex. CC-BY)
- Your use can be considered Fair Use
Always cite your source.