Extra Resources on Copyright and images:
Free Images (free images, no citing)
Pixabay (free images, no citing)
Pexels (free images, no citing)
MorgueFile (free images, no citing)
Unsplash (free images, no citing)
Creative Commons Search Page (aggregates many, many websites with creative commons images - be sure to cite correctly)
Wikimedia Commons (has many public domain images as well. Has a huge amount of historical images. Be sure to cite correctly)
USA Gov (just add the link to cite)
No Need to Cite the Image:
If you took the photos yourself
If you got the image from a free image website
If you used the Explore Button in Google Apps (or Insert, Images, From Web)
If you got it from a .gov website like NASA.
Must Cite the Image:
If you got it somewhere else online AND it has a Creative Commons license
Usually adding the link to the image where you found it, is OK in middle school. Save the more formal citation for high school and college.