@3dk offers some really great jumping off places:

I'm a noob too, but this is how I would start my search to automate adding invisible digital watermarks to images:

https://www.startpage.com/do/search?q=add+watermark+invisibly

https://www.startpage.com/do/search?q=automate+image+manipulation+python

https://www.startpage.com/do/search?q=Add+watermark+python

https://wiki.archlinux.org/index.php/List_of_applications#Image_processing

https://wiki.archlinux.org/index.php/List_of_applications#Raster_graphics_editors

Thank you, this is fantastic and super informative.

aw gee, thanks for the help!