This is a subject I admittedly don’t keep up with, but there is experimental software available for both webcams and RTSP.
I don’t know if the Webcam firmware was ever released for the V3, and I only posted a link to the V3 RTSP firmware (there is also a V2 version). In any case there are several discussions on the board about both:
While yes, the RTSP firmware is available as a separate installation for the V2 and V3 cameras, they still will want Internet access. To have a true IP camera you’d need Dafang Hacks firmware on the V1 or V2. I assume the webcam firmware would not suit your purposes as it requires a USB connection.