Can you ask them? Make the user take a pic of the store, then check the EXIF for the timestamp. The pic should be very easy to shape-compare with other submiss

Can you ask them? Make the user take a pic of the store, then check the EXIF for the timestamp. The pic should be very easy to shape-compare with other submissions of the same store (hardware doesn't move much, as opposed to faces), and the pic should never be exactly the same (refuse submitting twice the same pic). Other solutions require the participation of the store: Dynamic QR codes, microphone authorization, or a website on the store's Wifi internal network.