A strobe gif in an email is illegal, really? How are you going to prosecute that?
Well it depends on the state. In most states you bring charges to a grand jury which examines the basis for the charge and issues and indictment, then Bob's your uncle. In some states you can file what's called an "information", which leads to a preliminary hearing. Either way, you have to show that you have some basis for prosecution, and then it's on to the jury trial.
In the jury trial, you have to convince ALL twelve jurors that the accused is guilty beyond any reasonable doubt. To do that you have to show two elements:
- actus reus
- An actual act, omission, or possession which contravenes the law.
- mens rea
- "Guilty mind" -- intent to do the unlawful thing.
What's confusing to people here is that the same actus reus can be criminal or innocent, depending on intent and awareness. If someone slips a piece of shoplifted property into your pocket, your possession is unlawful, but you aren't aware of it so you don't have mens rea. If you serve someone with a deadly nut allergy food that will kill him, whether that is attempted murder depends on whether or not you know he will be harmed.
So to answer your question, to prosecute sending a gif, you have to show that the person sending it was aware that it would cause harm at a minimum. If you can show he intended to cause harm that's even better. In this case, the offending gif was accompanied by this text:
You deserve a seizure for your post.
Saying that seems amazingly stupid. But the delusion you can escape legal responsibility for assaulting someone by using means that wouldn't work on everyone is pretty stupid too.