Stock images are often staged, not natural, lacking spontaneity. Images with a creative commons license on Flickr are an excellent alternative, with one drawback: it is a bit harder to find the right image.

Here is what I do. Now and then I take a Flickr "deep dive" and just randomly browse/search images not using a functional key word such as "chair", "pilot", or "apple". Rather use characteristics that a photographer would use to describe an image. As an example, see what a range of beautiful images comes up when searching for "focus".

Browse through the images and bookmark them or save them to a tool such as Evernote for later use. An example, a very detailed image of the Manhattan Bridge by See-ming Lee.