Images and documents can be added to Canvas Quizzes and Assignments. For example, an image can be uploaded and embedded in quiz instructions or the question body of a multiple choice question in a quiz. If you want to make the images / documents only visible to students when the assignment / quiz is available,  the permission “only available to students with link” needs to be set for these files. And these files will be hidden in Canvas Files. 

If the permission for a folder is set as “Only available to students with link”, all the files are hidden when they are uploaded to the folder and inherit the same permission. In addition, there will be no notifications sent to students for the files that are hidden