What is the best way to get very relevant non-copyright images for articles?

What is the best way to get very relevant non-copyright images for articles? I have setup the following image importers in settings, but which one is ECHO importing from?  Does it randomly choose which site to pull from? MorgueFile, Pexel, pixabay. Is "enable broad image search" not a good way to get relevant images?  How do I get non copyright images that are very related to the title?