Basically I would like to plug in my Android phone to a Linux computer and have it appear as a USB video device such that it can be seen in /dev/videoX and can be opened to capture video / images using the phone's camera.
Are there any specific hardware / Android limitations that would make this infeasible?
What are the general steps involved in making this happen (if at all possible)?
Can it be done as an Android app or does it require completely modifying the Android / kernel?
I assme you want to use your Android Phone as Webcam? There's an App for that. I believe Droidcam was it called. Check it out here: Droidcam Instructions for Linux
As far as I know, /dev/video0 , /dev/video1 and so on are devices that show up for drivers are based of the V4L2 (Video For Linux Version 2) subsystem.
What are the general steps involved in making this happen (if at all possible)?
The naive developer way would be to write a USB driver that recognizes your phone and registers a V4L2 driver for it. It could be an empty driver.
Can it be done as an Android app or does it require completely modifying the Android / kernel?
I suppose you could build a loadable module (ko) for this.
Please re-purpose your question to what you really want to achieve, as this may not be the right way of doing this.
