Why is P9_14 GPIO input using Adafruit's library giving me -1227689624 on my BeagleBone Black?
That photo of the pin names is wrong. P9 is the one closest to the power jack. Look at your bbb, it has P9 and P8 printed at the end of the headers. 
If the photo of the bbb connected to a breadboard is yours then your input is connected to P8.12