If the focus of the observation seems to be something made by humans (e.g. plastic flamingo), I mark it human.
If the observer labeled the observation for a species that really isn’t there, I mark it “no evidence of organism,” meaning “no evidence of that organism even though there may be other organisms in the photo. For example, a photo labeled as a bird and there is no bird though there are lots of plants. Usually. If there’s another species that can be easily identified from the photo, I may try to shift the ID to that one, with or without asking the observer. I’m most likely to shift the ID arbitrarily if it’s an older observation and the observer seems to be gone.