How can I obfuscate a small section of a image on macOS?
Preview, built into macOS, has a few tools for doing this. First, open the image in Preview (the default app for images), then choose the Annotate button on the toolbar.



Options for obfuscating:


Use a selection tool to make a selection on the image, then press Backspace to delete that area. For filetypes which support transparency, the area will be removed, otherwise it will be saved as white.




Use a rectangle or other shape and set a fill colour.