The most difficult part in setting up a blog or website are the images. Images of your post or your page tells exactly what it is about. Using a wrong image misinterprets your intention for the page or the post. However, finding the best image to use for your site is not as easy as doing a quick search about it. It might be prone to copyright infringement and can lead your site to a disaster. If you want images that are royalty-free and you can use whenver you want here are some of the best sites to look for it.
Have a look at the best stock images here: http://www.wpexplorer.com/wordpress-image-resources/