Seashore (a severely gimped GIMP) is a decent simple editor for OSX.

https://github.com/robaho/seashore

Interesting. I may figure out a way easily to get a full screen of white (full-screen in a browser on a blank HTML page?) to hackily print screen to use that as MacOS "paint", heh.

Those are the same markup tools found in Preview.

If you open an image or PDF in preview, just go to View -> Show Markup Toolbar

Or you can choose tools right from the Annotate menu.

You can do it from Preview. You can even CMD c a video frame in QuickTime and in Preview select File>new from clipboard.