This answer is probably very Man, but I don't think any experience that a person capable of consent could have online would equate to rape. Rape is about force, about lack of control, consent, or will. That would never be the case, because ultimately we all have a simple option: turn the computer off. With such a safety valve, there's nothing that can really happen without some level of consent on our parts.

A sudden, offensive message/picture/etc could violate that somewhat (there's still the question of pre-consent by participation). There could something we don't wish to see, but do...but again, I can't really compare that to rape; it's just life -- bad things happen. Besides, I exist in a country based (somewhat arguably) on free speech -- so even offline, this is not rape, just rights.

The only real exception I see are those incapable of consent -- that is, kids and the mentally ill, who may participate in something without fully comprehending what they're doing. In such a situation, yes, I strongly feel that rape is possible and should be punished. As for legal action per se...that's a rough question to ask an anarchist