Consolidate image serving in examples and test/manual

We currently use a variety of images from all over the internet, including picsum, placekitten, placepuppy, etc. Our images in `examples/img` are slightly out of date. We should revamp the images in `examples/img` and possibly document recommendations for them so we can serve all test images within the repo.

Start by inventorying image references in examples and test/manual, then compare them with the assets in examples/img. The work is done when the outdated examples/img images are refreshed, test images can be served from the repository instead of varied external hosts, and any image recommendations are documented if that scope is retained.

Written by the indexing model from the issue text.