I have an unused C wire hooked up to thermostat and have no idea where to connect it to the furnace for power
Based off the first picture, it looks like the blue wire fell out from the wirenut next to it with the black and white wires going into it. 

That should be the common side of the 24 volt transformer used for the AC, which is what you probably want to be using for C.

Test to see if that all makes sense first rather than just connecting it. I'd rather not make your problem worse! 

I don't know what to tell you about the second picture though, so determine if adding the blue wire to that wirenut makes sense, and if it doesn't just down vote this answer.