Okay, but as proof, it isn't really much, is it?
I mean if you can prove that you posted something before me, that's more or less proof that you have more claim than me (though even that's not absolute ... you, for example, might have received a pic from me in an email, posted it on Tuesday, and when I got around to posting it on Friday, you already had three days advance over me in terms of posting date. Yet the pic was still mine, not yours).
But your earlier posting date, whatever edge it gives over my claims, is still not proof that you didn't take the pic from somewhere else.