Nor to me - but it doesn’t make a lot of sense with images either.

Text is literally just an array of numbers (Unicode character points); where do you put “invisible” watermarks there? Images are, likewise, a three-dimensional array of pixel color values; while it’s possible to very slightly vary those color values and call that “watermarking” (similar concept: steganography), how does that not get lost even unintentionally on the first lossy compression step?!