A while back I used a selfie stick on my Microsoft (Formerly Nokia) Lumia Windows Phone.
I needed an extension pole to take pictures that were up high, and in places I could not reach.
In doing so I setup my phone to automatically open my Lumia Camera app.
After sometime went by I could not figure out how to change this.
I did not want my phone to open the camera every time I plugged in a headset or Aux cable.
So after searching the web I could not find any information on where this was, I searched all through my settings with no avail.
I finally found that it is an app that comes default on your Windows Phone called Gadgets.
Open the Gadgets App there you will find the settings to change what happens when a certain device is plugged into the headphone/headset jack.
You can select a device to automatically open an app, or select the device to NOT open an app..
I hope this info. has been helpful, as I was getting frustrated with the issue.