Answer:
IS LEGAL:
Copying a quotation from a website and citing the source.
Receiving permission from a photographer.
Downloading a videio in the public domain and using in a presentation.
IS NOT LEGAL:
Copying a photo from a website and then using it without requesting permission. it's not legal because the autor of the picture or the company that owns the website has its copyright, therefore you would be stealing their intellectual property.
Copying content from a Wikipedia article, changing the words, and using the text withtout searching the source. its ilegal because its considered plagiarism.