Schools have a duty of care to their students and there are plenty valid reasons to not want your face on the internet. E.g children who have been adopted from abusive families, threats made to children or their parents etc.
You can be polite about it and not confrontational. Just tell them that you’re unable to provide further information on it at the moment, but that you need them to take any photographs of you off the internet and refrain from posting anything in the future.
Let them fill in the blanks with whatever story they want.
I have tried to use the open source CAD programs, but they never worked that well for me.
SketchUp is good, for what it is, but again it’s never been for me.
If you want 2D like AutoCAD then I have found SolidEdge from Siemens to be good. There is a free version, and I think a paid one too. I only used the 2D version but a quick search just now seems to show a community edition of the 3D too.