In InCopy it's possible to place notes inside a text. But if the editor wants to say: Please make the image darker and sharper, how to do this? It's not possible to place notes on an image … Thanks!
There isn't a standard way to do this as the "Notes" tool only works in text. However, I've seen people resolve this by placing empty text frames over images or placing empty text frames outside of the content where users can comment on things using plain text.
If there are captions, they can go there, too.