[Syrphidae] Querie: when to accept a species as new to the fauna?

[eckvana]

Having the situation at hand of a species, in this case _Mallota
fuciformis_, photographed in a country where it was not recorded yet.
The identification is unmistakable. 
Is this enough to report it as new to its fauna? 
So far I have never accepted photographs as proof.
What are your ideas about this? Is a voucher specimen always necessary?
Is there a clear guideline for this? 

Yours sincerely,
André van Eck
Tilburg, The Netherlands 
 
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