Evidently this solution is stretching the idea of what makes images "different". Each corresponding pair of panels would be parsed as identical in any other case. It is worth noting that if you view this Problem on a template, the solution no longer applies at all.
Left examples are not required to be valid, as long as their solution doesn't apply in the traditional Bongard Problem format (6 panels vs. 6 panels, all one image). Additionally, they do not necessarily have to be rendered invalid by being viewed in the template format, but their solution does have to be altered. In some cases left examples are simply Problems whose solution is specific to the computer medium (BP941), however some examples have more profound solutions that the pen-and-paper template medium is too restrictive to represent (BP854).