To add an object to Favorites, right click on the object and select Add to Favorites. In Image Editor you can add an object that is on a project to Favorites.
Select the appropriate folder or press Add Folder to create a new folder.
To organize your favorites, press the Organize button on the Favorites tab.
In Organize Favorites you can move objects between folders and remove items from favorites.
The same favorites are used for both Image Editor and Planner.