I’m not sure you can get the accuracy you want by making a series of cuts around the board and taking a photo of it. Even with the high resolution cameras, I just think detecting the cut points really accurately will be difficult. Trying to hit a 0.5 mm accuracy in results is challenging. That’s why I’ve taken to using a printed calibration pattern. I got three ANSI E blueprints printed at Staples for $21 to cover my board… seems cheap enough. The only thing else that’s needed is a cheap usb endoscope and something to get the endoscope perfectly centered in the router body (I’m using a turned block of wood at the moment but need to improve upon it).