One obvious alternative is to use a real optical mouse, but move the surface next to the sensor. This would be easy with any of several motorized mechanisms, e.

One obvious alternative is to use a real optical mouse, but move the surface next to the sensor. This would be easy with any of several motorized mechanisms, e.g. a turntable -- but that would be bulky, most people do not actually have a turntable, and many cheap implementations would make noise. That makes me wonder what would happen with an optical mouse atop a tablet, displaying a slowly-panning video of a texture. However, there are a few obstacles. First, Google tells me that optical mice have frame rates of 1.5 to 5 kHz. That's very fast. It probably makes the optical flow problem easier, since there's less change between frames. But it's also much faster than the, say, 60 Hz refresh of a tablet's screen. I don't know what a bunch of "stairsteps" in the position signal would look like to the mouse. Second, there's the issue of wavelength. Google brings me optical mouse sensors with sensitivities in the 832 - 865 nm range, i.e., in the infrared. Visible red is around 740 nm. Looking at this chart [1] and extrapolating just a tiny bit, it seems that LCDs have almost no emissivity around 850 nm. So this probably would not work. Whether an LCD with an infrared backlight would work is left as a question for another time. What might be easier still, would be to somehow hack the USB device itself to spoof the vendor and product ID. I don't know how to do that myself, but it might be easy for anyone who's familiar with USB device development. Of course, this is a silly arms race that it wouldn't actually be worth participating in, but it's amusing to consider what you could do. I heard a story of an employee health plan that issued pedometers and issued cash rewards for higher step counts. In short order, one employee had put his on a clock pendulum, another had secured the thing to the collar of his hyperactive dog, and a third had hacked the thing to display all nines. [1] https://www.displaymate.com/Spectra_4.html https://www.displaymate.com/Spectra_4.html