Unable to remove pictures in chat

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I have noticed on occasion that pictures can't be removed from chat, with the reason given being along the lines of someone else having uploaded the same picture. I'm having troubles understanding why this should be an issue in the first place. Could someone explain?

 

[ViXxXeN]

Umm, what?

 

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Most recent example was yesterday when a user was trying to remove a selfie they had posted in chat, but the system said that they couldn't and needed to contact a moderator, none of which were online at the time.