This thread may be of interest, to see and refer to what others have done previously.
If you’re wanting to draw custom annotations on the image then you’ll need to either do that on the camera/RPi side and encode the annotated images into the video stream that gets sent to the topside, or send the annotation data separately and use it to draw the desired annotations at the receiving end.
The latter approach is likely preferable in the long term, although it could be somewhat complicated at the moment in a software like Cockpit, because it’s currently lacking dedicated widget overlay support. That said, it should already be possible for an OAK camera BlueOS Extension to provide an annotation-drawing widget to Cockpit as an iframe with a clear background, which could then be manually moved and resized to fit over the relevant video stream widget 