add warning message to make sure image capture canvas attributes aren't removed

lms/templates/verify_student/photo_verification.html

@@ -93,6 +93,8 @@
                     </div>
 
                     <video id="face_video" autoplay></video><br/>
+                    <!-- Don't remove the width and height for the canvas or the clipping will be off.
+                         Placing it in CSS does not work. -->
                     <canvas id="face_canvas" style="display:none;" width="640" height="480"></canvas>
                   </div>
 
@@ -177,6 +179,8 @@
                     </div>
 
                     <video id="photo_id_video" autoplay></video><br/>
+                    <!-- Don't remove the width and height for the canvas or the clipping will be off.
+                         Placing it in CSS does not work. -->
                     <canvas id="photo_id_canvas" style="display:none;" width="640" height="480"></canvas>
                   </div>