Attendance is one bit of information (present/absent). Perhaps you can add exact time of entering and leaving which would make it a couple of dozen bits.
There is no need to record more information than this. The expectation of privacy is exactly this: that any information that is not needed is not recorded.
Human teachers are unable to capture or keep recorded all the extra information they see with their eyes. Cameras do.
That depends on the person, who tracks attendance.
If the teacher sells attendance reports (together with detailed lesson transcripts and audio recordings) to Google, Amazon, Netflix, US and Russian governments, all major data brokers and The USA Association of Rich Pedophiles, all at the same time — yes, there is no difference. Otherwise there is a substantial difference.
It is amazing, that a person, directly reporting such detailed information to elsewhere, would be considered a pervert and criminal, but using an automated camera to do the same thing is somehow alright?!!
Seriously though, where exactly is the privacy if attendance is taken either way?