I'm just gonna add this for completion, DroidCamX can be installed on a smartphone and its cameras will act as an IP camera. DroidCamX also has a Linux package that will make the connected phone show up as a V4L2 device. You can connect the phone over USB or over LAN in two ways (PC connects to phone or phone connects to PC).
Now obviously a phone isn't ideal for running 24/7 but since this is about privacy I thought it's worth mentioning.