No C Wire Terminal on Furnace
Your best clue is to observe that the 24VAC output transformer is labeled as follows:



The secondary is indicated to be the BRN and RED wires out of the transformer. One of these is the one that provides the power connection to the thermostat and is most likely the RED one that exits from the wiring box and connects to what looks like the skinny RED off to the thermostat. 

The BRN (brown) wire from the transformer is what you are going to want to connect to the skinny blue wire to the thermostat. It is a bit hard to see from the pictures that you provided,  but it looks like the BRN wire is connected out of the wiring box as also a BROWN wire that is connected a wire in the smaller control wire cable (which appears to be supporting part of an air conditioner unit). 

Carefully check and trace the transformer secondary wires to see if they are as I described above. If so you should be well on your way to getting your smart thermostat operational.