The title sums up a lot of what I have to say about this. Pexels is a searchable website offering free photos with a Creative Commons Zero (CC0) license. Photos are displayed as an “infinity scroll” on the home page or you can use their search. Once an image is found you can download the high-res copy. In the case of the raspberry image I’m using for this post it downloads as an 8MP image (2.07MB JPG).
Give it a look and let me know of other sources you might like to use.