The sensor forms an image and OpenCV detects the actual touch configuration. It appears you can use the raw data from the Arduino, too, but it might be a little harder.

If you’re ever hunting for a touch sensor but can’t get your hands on one, [Alan Chatham’s] tutorial on simple DIY capacitive touch sensors might be just what you need to keep things moving ...

Created by the parts supplier and Arduino tutorial creator Adafruit, the camera is built using an Arduino, an Eye-Fi Wi-Fi SD card, a TTL Serial JPEG camera, and a few other parts.