You cannot see your own crown properly, which is exactly why crown thinning sneaks up on people. A hand mirror over the bathroom mirror gives a rough look, but the angle and lighting change every time, so comparisons are guesswork.
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You can't see your own crown, which is exactly why it's the last place people notice. Two honest options. Have someone photograph the back of your head under an overhead light, hair dry, and parted the way you normally wear it. Or use your phone's timer on a shelf behind you. Same light, same parting, same distance, every time. Anything else is comparing two different photographs, not two different months.
The Uberhair hair check solves the angle problem with guided capture: the camera walks you through the overhead positions a doctor needs, and those photos go to the network doctor you choose for an initial assessment — from home. Tracking the crown over time is done at the clinic with GroTrack imaging.