NASA has a huge media library full of images, soundand videos, which you can access for free and use as you wish.
NASA has occasionally offered one small part video and images to the public, but recently, brought your entire library to your disposal, through its website. There you can search by some term, just like you do on Google.
For example, a search for Pluto returns 543 different results, including a large number of images, nineteen videos, and nine audio files. Most results also include a short description with each video, photo or clips so you know what you are seeing.
If you are looking for something specific, search results may also decrease by year. The oldest content available on the NASA site is from 1920, while the most recent content is from the year we go through. A slider lets you select the desired time window for your search, or you can leave it wide open to see all of NASA's material.
The best part is that you can use the collection as you wish. There are rules for non-commercial use of NASA media, which according to them the content is generally not protected by copyright. You may use this material for educational or informational purposes, including photo collections, manuals, public exhibits, computer simulations, and web pages at Internet. This general license extends to personal websites.
If you want to use the content commercially it is not so easy and requires contacting NASA Multimedia Division in Washington DC.
