Pensieve = Security Camera?

[vmonte]

No: HPFGUIDX 102813

Alice:
But this would mean that having a Pensieve would be like having 360
vision and senses all the time - albeit only in retrospect. Wouldn't
people USE that a lot more? Just one idea: the examiner could look
into his Pensieve after the exam and check whether anybody had been
cheating, talking etc.
I hate it when JKRs ideas seem be logically faulty, we must find
another solution...

vmonte responds:

Maybe this wasn't Snape's memory of the OWL day.  Maybe they were 
Sirius's.  page 646, US version:

"I was watching him, his nose was touching the parchment," said 
Sirius viciously. "There'll be great grease marks all over it, they 
won't be able to read a word."

Maybe that is why it appears that the penseive recorded more 
information than Snape could have possibly heard and saw.  It was 
really Sirius's memories.  Or someone, elses.

vivian