How do you invert a black and white photo image on a Mac?
In this earlier Post (from 2015)...
How do you invert a black and white photo image on a Mac?
...the answer required the person to have Aperture, but the basic methodology suggested also works with Preview! This method is slightly different than the method they suggested. Instead you use the Toolbox tool of the Preview app, then adjust the "Black" slider and the "White" slider as shown in the images below:
MacBook Pro, OS X El Capitan (10.11.3), The Apple Preview App