Assume that most works you want to use are copyrighted and need permission.
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.