TidyUP scans quizzes, including any questions that are used in the quiz. However, since TidyUP does not scan question banks due to limitations with the Canvas API, any questions that are not associated with a quiz will not be scanned.
Please note that if an image is added to a quiz question while working in question banks, Canvas gives the image a source path to the question bank files and not the course files. This means that TidyUP will show the image as unused in a course scan, even if the question is later added to a quiz. To avoid this problem, add images to quiz questions while working directly in the quiz itself so that the image has a source path to the course files and TidyUP can see it is being used in that quiz.
If you suspect an unused file may actually be used in a question bank, you can manually verify whether or not it is being used in a question bank before deleting it. The fastest way to do this is to go to the Canvas course menu>>Quizzes>>Manage Question banks (in the overflow menu)>>question bank. You will see previews of all the questions in the bank. The question's directions are included in these previews, so you should be able to tell if an image or other file is being used in a question. To view the answer choices, check the box that says, "Show Question Details".