A slightly odd question, but hopefully a good one. I came up with a scene in a book of mine where the main character (a student at a modern school) is at a large school assembly. Midway through, someone hacks the screens and projects nude photos of himself on them, showing the photos to pretty much everyone there. I’m mainly wondering what would happen immediately after, and what the school staff would do.
Your phrasing left it unclear so I just wanna make sure: the hacker projects nude photos of himself, or the main character?
Probably they have the IT guy shut down the network, call in campus police and local authorities and start an investigation. For most locals, it is illegal to publish nude photos without consent so if the hacker is caught they would be criminally prosecuted. They could also be sued for damages in civil court.
And if the person in the photos is a minor, it's a much more serious crime. As for the staff's immediate reaction, I imagine they'd be just as shocked and unsure what to do as anyone else. Maybe someone particularly quick thinking would unplug the projector? Or just put a hand over the lens?
How is this related to blackmail? Blackmailers ask for money in exchange for NOT showing embarrassing photos. Did you leave out a key plot element, such as the hacker having attempted to blackmail your MC and the MC refused to pay?