He found out about the photograph from Ginny at breakfast.
The first indication was Neville, who came down from the dormitory slightly later than usual with an expression that was trying to be normal and was not quite managing it.
'Did everyone get one of these?' Neville said, and put the envelope on the table.
Around the table, in the specific cascade of people checking things they had not checked yet, four more envelopes appeared. The Witness seal on each one.
'The Witness,' Hermione said, in the voice she used when she encountered something requiring immediate categorisation.
Harry picked up his envelope and looked at the seal. His expression had the quality of someone who knew what was inside and was choosing not to show that he knew. He caught Ron's eye for approximately one second and then looked back at the envelope.
The photograph was, by any measure, the right one. He knew this from watching the table receive it — the recognition that moved through each person as they looked, the particular stillness of seeing yourself in a room you remember being in, documented by someone who had been paying attention.
Neville looked at the photograph for a long time. 'You can see everyone,' he said. 'All the tables. All the way to the back.'
'The perspective,' Hermione said, examining hers with the systematic attention she gave things she found genuinely interesting. 'This was taken from the doorway, not from inside. Someone stood in the doorway at exactly the right moment and wasn't seen by anyone.'
'The Witness,' Lavender said. 'Who is the Witness?'
This produced a conversation that ran for most of breakfast and arrived at no conclusions, which was correct. He ate his toast and listened and occasionally offered observations that neither confirmed nor denied anything.
At the staff table, McGonagall had her photograph propped against her teacup and was looking at it with an expression he could not read from this distance and would have liked to. Dumbledore was reading the back.