This has been a long term discussion in the exhibit industry. But I think the question is really slightly different.
Let me put this out there. A graphic designer I know has a literal photographic memory. She retains 100% accuracy of anything she chooses to recall. So, if she walks onto the show floor and looks at your booth, is her accurate retention of that image unethical?
I think not.
So perhaps, capturing a photograph of the display is not unethical.
The ethical question is in what you do next.
An old professor of mine once said “Using one person’s idea is plagiarism, using 20 is research.”
If you duplicate something for personal gain, that is unethical. See: Chinese Manufacturing in the dictionary.
If you use the concept/design/execution as a starting point for your own journey, I believe there is some grey area as to how far you need be from the original to have created an individual element.
If you, like my company, encourage all your employees to develop a visual vocabulary, and as part of that to photograph things that affect them – a great sign, a great building, a lovely architectural element, a striking exhibit – then you are creating an encyclopedia.
And if you proceed from that with integrity, then you look into the encyclopedia for ideas, executions, details that you can employ in your personal execution of a design.
Chime in – What’s your perspective? Who are you – designer, exhibitor, marketer, manager?