Masturbating with pictures, objects, etc. is pretty common. Let your son know he can come to you with questions. To make things worse, he was holding women's panties up to his face, I assume, smelling them. He said he ordered the used panties from a web-site. I had never heard of this before, and frankly, it grossed me out at first.
Guys like to experiment.
Masturbating with pictures, objects, etc. is pretty common. Repeat violators of healthboards policy will be permanently barred from the boards.