Even if the acts are lawful, the thing you want to avoid with a 17 year old is
is taking pictures/ video etc.
In this situation, if anyone involved is not yet 18, then that's child
pornography.
Everyone being 16 or over doesn't matter.
Everyone giving supposed consent to being filmed/ photographed doesn't matter.
If anyone is under 18, then it's still child pornography.
So yes, it is certainly possible for a sexual act to which everyone has validly consented,
to still be child pornography.
Now, lets talk about offences.
Producing child pornography can be an offence.*
Possessing it can be a separate offence.
Distributing it (sharing it, posting it, forwarding it) can be a separate offence again.
A person can commit all three, or any one, or any two, of those offences.
A person can be an accessory (before or after) to any of those offences,
and/or can be faced with conspiracy, and/or with what used to be called "aid and abet" type offences.
And that's just the Crimes Act and
Criminal Code offences.
Space does not really permit discussion of the telecommunications offences,
nor the grounds for civil action for
defamation.
Further, pics and video that a person has taken/made/shot can be used as
both
evidence in the child pornography
prosecution, and potentially also as evidence
in a prosecution for any acts depicted which are themselves offences.
As to penalties - anything from a bond to more than ten years in
prison.
It depends on the facts and circumstances of the offences, aspects of the offenders,
and the technicalities of the individual charges.
That said, it tends to the harsher end of the scale, even for young people.
Now, here's the kicker.
A child can commit theses offences - even when the pics or video is of themselves.
Don't say you haven't been warned.
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* This includes, but is not limited to, taking pics or making video.
It also includes media like
Skype (recording and just using),
as well as using
Snapchat and similar products,
as well as both transmitting and, separately, recording
streamed video such as a webcam.