[fprint] Elan 0x0907 driver

[Igor Filatov]

Hi list,

I've written a driver for Elan 0x0907 fp scanner. I don't know which
model it is but it's marketed under various names for ex. Cobo C2
https://hardzone.es/app/uploads/2017/04/Cobo-C2-01.jpg. You can get it
on AliExpress for about $25.

https://github.com/iafilatov/libfprint/commit/e19f7e339c65e5d001f3117b4a3308ee9234e492

It seems to work in general but there are some issues. First, it's
technically a touch sensor but the images it produces are so small I
never got more than 5 minutiae from them. So I'm using it as a swipe
device instead. But it needs a steady swipe to produce a relatively
decent image (I'm getting best results when staring the swipe from the
finger tip). And I suspect that the motion compensation subroutines
weren't built for this kind of use so the image has rough edges which
could harden minutiae detection (dunno, it's my guess). I had to lower
the threshold to 20.

I'd really appreciate feedback about the driver. I wonder if it's
worth trying to improve the image assembling logic to get more
reliable verification.