You do not need permission if you are using something that is not copyrightable or is in the Public Domain:
The Public Domain Review: An online journal and not-for-profit project dedicated to the exploration of curious and compelling works from the history of art, literature, and ideas. The focus is on works now fallen into the public domain, that vast commons of out-of-copyright material that everyone is free to enjoy, share, and build upon without restriction.
Creative Commons provides CC licenses and public domain tools that gives every person and organization in the world a free, simple, and standardized way to grant copyright permissions for creative and academic works; ensure proper attribution; and allow others to copy, distribute, and make use of those works.
There are 6 difference CC license types and a CC Public Domain Dedication tool:
CC BY: Includes the following elements:
BY - Credit must be given to the creator
CC BY SA: Includes the following elements:
BY - Credit must be given to the creator
SA - Adaptations must be shared under the same terms
CC BY-NC: Includes the following elements:
BY - Credit must be given to the creator
NC - Only noncommercial uses of the work are permitted
CC BY-NC-SA: Includes the following elements:
BY - Credit must be given to the creator
NC - Only noncommercial uses of the work are permitted
SA - Adaptations must be shared under the same terms
CC BY-ND: Includes the following elements:
BY - Credit must be given to the author
ND - No derivatives or adaptations of the work are permitted
CC BY-NC-ND: Includes the following elements:
BY - Credit must be given to the author
NC - Only noncommercial uses of the work are permitted
ND - No derivatives or adaptations of the work are permitted
The Creative Commons Public Domain Dedication:
CCO (CC Zero) is a public dedication tool, which allows creators to give up their copyright and put their works into the worldwide public domain. CC0 allows reusers to distribute, remix, adapt, and build upon the material in any medium or format, with no conditions.
Internet Archive: Moving Image Archive: Digital movies which range from classic full-length films, to daily alternative news broadcasts, to cartoons and concerts. All videos are either licensed under one of the Creative Commons licenses or are in the public domain.
Internet Archive: Prelinger Archvies: Goal is to collect, preserve, and facilitate access to films of historic significance that haven't been collected elsewhere. Includes films produced by and for important US corporations, nonprofit organizations, trade associations, community and interest groups, and educational institutions.
Khan Academy: Offers practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom.
>>Kahn Academy Terms of Service
The Library of Congress Guide to Public Domain Films
Library of Congress: Moving Image Research Center: Provides a number of collections of early motion pictures, many of which are in the public domain.
New York Public Library: Public Domain Collections: Over 180,000 items in the NYPL digital collections are in the public domain.
Open Images: Open media platform that offers online access to audiovisual archive material to stimulate creative reuse. Footage from audiovisual collections can be downloaded and remixed into new works.
OpenCulture.com: Watch 4,000+ movies free online. Includes classics, indies, film noir, documentaries and other films.
OpenVideo Project: A Project of the School of Library and Information Science at UNC Chapel Hill. Purpose is to collect and make available a repository of digitized video content for the digital video, multimedia retrieval, digital library, and other research communities.
PBS Learning Media: PBS has curated free, standards-aligned videos, interactives, lesson plans, and more for teachers.
Pixabay: Community of creatives, sharing copyright free images, videos and music. All contents are released under the Pixabay License, which makes them safe to use without asking for permission or giving credit to the artist - even for commercial purposes.
Pond5: Free video stock footage. Not everything on Pond5 is available for free.
Public Domain Movies: Feature films in the public domain
TED Talks: Nonprofit devoted to spreading ideas, usually in the form of short, powerful talks (18 minutes or less). Covers almost all topics — from science to business to global issues — in more than 100 languages.
>>TED Talks Usage Policy
USA.gov YouTube Channel: The official YouTube channel of the U.S. Government, linking to videos across government. Most content produced by the government falls in the public domain.
Videvo: Free stock videos and motion graphics for use in any project. You may use these video clips free of charge, in both personal and commercial productions. Video clips that carry the Creative Commons 3.0 license must be attributed to the original author.
Vimeo: Large collection of videos licensed under one of the Creative Commons licenses or the Creative Commons Public Domain Dedication. Note that many videos on Vimeo are under copyright and have not been licensed under any open license.
Wikimedia Commons: Media file repository making available public domain and freely licensed educational media content (images, sound and video clips) to everyone, in their own language.
YouTube: After performing a search for video content, you can "filter" by Creative Commons license to find content with reuse rights.YouTube has a large collection of videos licensed under one of the Creative Commons licenses or the Creative Commons Public Domain Dedication. Note that many videos on YouTube are under copyright and have not been licensed under any open license.