Create a device to detect object state
Your answers :-)


yes, it's possible and should not be too complex
for a simple prototype, you do not need an embedded device, just a PC with a webcam
a webcam with few megapixels should be enough
try OpenCV


After your prototype is ready, you can use a small PC-like platform.
Examples: Minnowboard, Edison, BeagleBone, RaspBerry PI 2, Arduino Yun, Galileo 2

A word of warning: depending on the expectations you have, you will have to pick more powerful models. Computer Vision is computationally intensive.
The examples I gave are roughly sorted by performance and, unsurprisingly, cost. OpenCV is available for many architectures, but afaik, it is particularly optimized for x86, since it's mostly sponsored by Intel.

Disclosure: I work for Intel, so I am more informed on Intel products, but by no means I'm trying to do advertisement, this answer is simply given to the best of my knowledge.