Beginner's question: opinion on cropping

I agree.

But this thread is more going: "What is art?" or "When is a photo art?"

I don't think an unintentional photo is a worse photo. As in your example the crop made it better imo.

the discussion is imo what set of rules one uses to judge own work and that of others, let everbody decide for themselves.

I like streetphotography, it's changing constantly (light,subjects etc) and at times you just press the shutter because it might be a keeper. At home sort them out and if composition can be improved I crop.

Not everybody will admit but I do, I took some shots that I find good based on 50% me and 50% luck.

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Cheers Mike