The hard truth about the N9: shared minibuses and CTM coaches from Marrakech to Ouarzazate typically stop only at the summit plateau and briefly at Aït Benhaddou. The four other stops in this guide are invisible from a moving vehicle and inaccessible when you have no control over the driver. A 6:30 am departure in a private 4x4 is the only way to work the entire road photographically in a single day.
There is also the question of waiting. The hairpin descent (km 115) can look mediocre at noon and extraordinary twenty minutes later when a cloud shadow moves off the slope. A private driver will wait. He will also know which villages accept visitors, which sections of road get icy in winter (and which do not), and whether the Telouet kasbah detour is worth it given your remaining light.
Most photographers who have driven the route independently say the same thing: the road is wide enough and the lay-bys frequent enough that you need no special skills to stop and shoot. What you need is the freedom to stop whenever you want. A guided private day trip from Marrakech that routes through Tizi n'Tichka to Aït Benhaddou and Ouarzazate costs roughly 1,200–2,000 MAD per person (indicative, depending on group size and return logistics), and is the most practical way to cover the photographic route without renting a car and navigating mountain road markings yourself.