How to get image with original resolution from camera video stream?

I need save image when any face detected and send picture to my backend.
In example [face_camera.html ](https://github.com/eduardolundgren/tracking.js/blob/master/examples/face_camera.html#L28) we have resolution with 320x240 but camera has resolution with 1920 x 1080 pixels
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How to get image with original or custom resolution ( 800 x 600 ) from camera video stream?

Start with examples/face_camera.html, especially the video and canvas elements shown in the issue, and trace how the camera stream image is captured. Done means documenting or demonstrating how to obtain an original or custom-sized image, such as 800x600, for sending to a backend.

Written by the indexing model from the issue text.