A check-in is just a weekly opportunity to score some points and ensure that you are keeping up with the course content. The requirements vary from week to week, but may involve responding to a survey, taking a brief online quiz, or participating in a discussion forum. They are due by midnight on the designated day.
Below are links to a series of images that are lossy-compressed using different quality settings. Open them in separate tabs of your browser, and then try to rate them in order from worst quality (1) to best quality (5). Submit your ratings here.