Automator macro run when image appears

I don't believe that there is currently a way to achieve what you want to do using Automator. HOWEVER, there is one commercial application that has been around forever on the Mac and I've used for countless years.

• • Keyboard Maestro $36USD (as of the date of this reply) - https://www.keyboardmaestro.com/main/

There is an action you can add to scripts that searches for an image you give it, on all screens, only one screen you specify, the front most window, and more. When it matches you can specify an action to happen, and while it is not matching you can have it execute something, or just leave it empty to keep looking. It is incredibly powerful the things you can do with it. I strongly suggest giving it a try. 😀👍

Lots of apps and services can place an image on your screen. Web browsers. Preview. Notes. LibreOffice. Etc.

Potentially using various sizes and resolutions, too.

There is no generic means to detect an arbitrary image being shown on macOS.

Not short of an immense computing effort involving scanning ongoing periodic screenshots.

There are ways to scan images for things (QR codes, faces, etc), but not scanning things (screens) for images.

Appears… where?