Need a new feature to prevent fake Confirmation for Submission for quizzes

I asked students to show the confirmation of submission for the online test before leaving the room. However, some students used screenshots of previous tests to be allowed to leave and then continued taking the test outside the room. In large classes, it’s challenging to verify the submission online. A useful feature would be to allow instructors to change the color, shape, or other identifiable characteristics of the confirmation for each test.