There are a number of reasons ClearCorrect requires patient photos. One of these is to accurately orient the patient's occlusal plane.
The occlusal plane is an imaginary curved plane formed by the incisal edges of the anterior teeth and the occlusal surfaces of the posterior teeth.
The angle of the occlusal plane varies from patient to patient. After scanning impressions the technicians must attempt to accurately orient the patient's occlusal plane before staging treatment from your prescription.
Without a photo of the patient smiling, the models may be oriented with the occlusal plane too flat or excessively tipped, causing the maxillary incisors to look like they need to be intruded or extruded. Note in the images below the difference when the occlusal plane is calibrated.
For further information on occlusal planes and digital treatment planning, check out the online article "Importance of the Occlusal Plane in Virtual Treatment Planning" by Dr. David Paquette.