1. Whatever kind of challange you prefer, the best way to give to competition a bit of professional - use your own models and scenes not downloaded or bought, some people here trying to do the best job they can, they waste a lot of time and what? Some users prefer, to make it in the shortest route that is possible, but it's not really funny.
I totally agree with that. For my own, as I want to show on my website only works made 100% by me, I build everything myself and never use bought or free models from other artists. My only exception is for some images used in background, and even for that purposes, there is always an important edition work on these images, and they are never displayed in their original form. It has been a difficult choice for me : going fast and focusing on the lighting and rendering of a pre-made object, or building new things from scratch. The second method is my preferred one, even if it was not supposed to be a modelling challenge, because I hate showing things that not fully belongs to me. It's my own philosophy.
Working in production for a client, with a short deadline is not the same as participationg to an artistic challenge, and so I agree that rules should be more constraining, even if the main purpose is to show the performances of the rendering engine. I could say over all if the goal is to show the performances of the renderer, because when using camera mapped images, lights and shadows are often already contained for at least a part in the mapped photographic textures, and so it is more difficult to see if the amazing result is due to the renderer or to the original shots used as mapped textures... At the extreme, one can map a photo on a plane and render this plane in Octane. He will not really infringe the current competition rules, but this kind of "scene" would look identical rendered in any render engine. So, I think that avoiding camera mapping would benefit to both artists and Octane.
Just my opinion.
French Blender user - CPU : intel Quad QX9650 at 3GHz - 8GB of RAM - Windows 7 Pro 64 bits. Display GPU : GeForce GTX 480 (2 Samsung 2443BW-1920x1600 monitors). External GPUs : two EVGA GTX 580 3GB in a Cubix GPU-Xpander Pro 2. NVidia Driver : 368.22.