Detecting certain objects

Here is what I am trying to accomplish: I need some kind of sensor that will recognize a certain object placed in front of it. The object could have some kind of receptor hidden but detectable by the sensor. Also would be perfect if that receptor would be not powered it's easier to hide and maintain.

This sensor should be able to recognize the receptor if only placed in a range of 2 to 4 feet in front of it.

I have seen somewhere something done in a room... the objects in the room had some kind of sticker attached to them, and thanks to that sticker, a system was able to map the exact position of the object inside the room... like a bar code or something...

Not sure what was the technology behind it... arduino, rasberry, etc... but seemed to be working.