Copyright gives creators of creative works (text, art, music, photography, sound recordings and films) the right to stop others from copying their work without permission.
As students, you can reproduce a proportion of a copyrighted work for research or study (approximately 10%). When you do this you should attribute the author, and provide a link to the original work when possible.
Some authors of images and videos make their work available without restrictions and this guide also includes suggested sites for finding open content.
More information is available in this student guide to copyright.
When you use someone else's creative work (images, audio, video etc.), you should give credit to the creator of the material (attribution), just as you should include a reference when using someone else's words from text.
You attribution should ideally include:
Title
Author/Creator
Source (URL to the original work)
License
If you aren't sure where an image came from, you can try a Reverse Image Search.
Some creators make their work available for reuse under Creative Commons licenses. There are 6 different licenses, which explain how the image can be re-used: https://creativecommons.org/share-your-work/cclicenses.
You can search the CC site for licensed materials, and it explains which license applies to the image or audio, how you can use it, and how you need to attribute the image.
Find Creative Commons images on Google Images
Find Creative Commons images on Flickr
Find Creative Commons videos on YouTube
Here are some libraries of images which have been shared for re-use.
Unsplash - Beautiful, free images and photos that you can download and use for any project
Visualhunt - High quality free photos in one place - most photos are CC0 license (do whatever you want), some are Creative Commons and Public Domain.
Burst - thousands of high-resolution, royalty-free images that were shot by a global community of photographers
New Old Stock - Vintage photos from the public archives. Free of known copyright restrictions
Gratisography - quirky collection of free high-resolution pictures
CSIRO science image - images from science and nature (creative commons)
Even though many of these images are free to use, it is always good practice to provide an attribution.