First of all, there's no reason why you can't have "glass people" of your own.   If it's for fan art, most publishers would leave you alone.  Commercially may be a different matter and it would always be best to consult a legal expert.  That said, transparent/ghostly/glass type figures feature in all kinds of things so I seriously doubt there could be a copyright on such a concept.

Anyhow, there's an XRay shader kicking about on the site and you should find a post about it a few pages back.

That said, your character is going to look really weird because you'll have the eyeballs and inner mouth showing, the back of the head and hair, clothes and any other accessories will also show up.  You'll get a hollow tube effect on all the figures, which  I doubt is what you want.  

If I understand your requirements correctly, you'd be better off rendering your characters separately from the main image, then pasting them as layers in Photoshop.  Change the layer opacity, add some Inner glow - or even a "glass" layer style - to get the effect required.

Coppula eam se non posit acceptera jocularum.

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