My neighbor secretly installed a covert LED camera in his backyard (even using a bug zapper as a decoy light/sound). It had a motion sensor trigger that picked up movement when we were on our patio and even in our bedroom, setting off a buzzing sound similar to the bug zapper but not the same (lower, muffled). Even more creepy-he had told us all about the bug zapper in the beginning of the summer as if to resolve any questions we might have about all the weird noises. We confronted him about it and he denied it, but was obviously very nervous and paranoid that we asked. Since then, he seems to have a security system that occassionaly chirps and buzzes--that we hear when we are in the backyard. What expectation of privacy do we have in our backyard in Illinois and is it a criminal offense?
Look at the following case, which I was principal defense counsel in. http://www.state.il.us/court/opinions/appellatecourt/2005/2nddistrict/april/html/2040170.htm You'll see that you don't have an expectation of privacy in your yard that will serve as the basis for an injunction preventing your neighbor from taking video of you. And, it's not a crime to film something outside, even if it's in your back yard. However, if he films inside your house, that is a criminal act and would be something you could get a court to enjoin.
Of course, he can never use an audio recorder, as that would constitute criminal eavesdropping under the current statutes. Hope this helps, but you may well wish to discuss the specific facts with a local attorney knowledgeable in this area.
Please be sure to mark the best answer to your question. My answers are general and do not form an attorney-client relationship. I'm happy to talk to prospective clients in my areas of concentration and geographical location.