One of the little known and used Apps in the macOS is Automator. It is a very powerful App, but at the same time it is not difficult to use. You can create all kinds of little Apps and Workflows with Automator including Folder Actions. Folder Actions are just what they seem. You attach an Action to a folder, when you drop something into the Folder it runs the Action on it. One common Folder Action is manipulating images in certain ways. This article describes how to setup a folder Action for converting an image to a different file format. But, you can run all kinds of different image manipulations using Folder Actions. I run one that re-sizes images to specific measurements. Folder Actions are handy, check out the article for an overview of how to use them.