Pixabay seems to be one of the best sites to obtain high-quality
images that can be used freely.

https://pixabay.com/en/editors_choice/

I've noticed that they only accept images starting at something
like 6 MP (at least 3000 pixels in width).
Is it likely they will bump that lower limit even more in the
future? Surely people are not going to print these pictures to
fill up entire walls?
I'd reckon 2 or 3 megapixel images should still be fairly useful
for many purposes if they are good pictures.

Thinking in particular of finding images useful to create digital
collages:

https://i.imgur.com/GiJFTRw.jpg