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A screenshot or a shot of someone's screen?
If the former, pull down the notification bar and look for this icon in the list. If you're unable to find it, please provide a screenshot of your open notification panel and maybe we can pick it out.
If the former, unfortunately you will have to ask the owner of the phone, as we do not discuss the violation of people's privacy or help those looking to get private information about someone else's device.
Beyond that a Google image search is your best bet.
Best wishes