What operating system do you use? If it’s Windows 10, they’ve recently rolled out new permissions for cameras and microphones and screwed up a lot of things. 
Work through this first and let me know if it’s still not being seen by LightBurn: Getting your camera to work in the hellscape of Windows 10
For the crop question, LightBurn does not currently have an image cropping tool. It’s something we’ll likely do after the pending release, hopefully for the next one.