How about a new Data Quality Assessment item or other ability that is only accessible to curators, which could be a catch-all for marking an observation as casual or hidden?
This way the user who notices the duplicate content should 1) first comment on the observation to ask observer to fix it, 2) upon lack of action, flag the observation for curation, then 3) a curator can confirm that it is a true duplicate, mark it as duplicate, which hides and/or casual-grades it, and resolve the flag.
I recommend curator-only access since as you mention, many users confuse “multiple observer dupes” as “bad”, whereas it’s totally okay if multiple people observe the same thing. And, it may not be a true duplicate after all.
The catch-all casual-grade and/or hide feature could also apply to cases where
- the observer uploaded several photos of completely different organisms and is also unresponsive to requests to separate them, and
- “inappropriate” observations where the user has been warned/suspended, but the flag would otherwise remain unresolved in perpetuity. Our only option for hiding grossly inappropriate content at this time is to mark them as “spam”, which isn’t ideal.