Finding royalty free pictures to use on websites and presentations can be problematic.
A Google or Bing search will turn up hundreds or even thousands of great images on a topic but even if your search includes words like “Public Domain” or royalty free, the results will be dominated by companies trying to sell you images, sites using images that don’t belong to them, sites that regard the pictures photos as their own property and more.
Sites with the word “free” in them seem to have some of the most intrusive ads and malware too … (that could just be my imagination)
I can’t approach the legal issues of whether an image is “free to use” or not… that is covered in depth in many places including at the site I link.
Still, if you’re in a rush, isn’t it best to look at a place first where the odds are that the images you find will be in public domain (at one level or another)?
The link takes you to a search for “Earth from Space”. Try a number of different specifically worded searches before you give up on finding what you want.