Can I open user's webcam directly from my php page without having permission from user?

Answer 1

No and why would you want that. Bit creepy don't you think?

Answer 2

no

Answer 3

It's called hacking

Answer 4

If answer is directly no then how CIA/FBI monitoring our every keystrokes? even our webcam also!
There must be a way. If a developer/engr. know the actual way then he might also stop it too. That's my point.