Where's the reverse light?
 

Would someone let me know where the reverse light is? Is it what I have circled in turquoise? Also, is the positive wire to the reverse light what I am pointing at with the red arrow?
https://cimg8.ibsrv.net/gimg/www.clu...b543c00cc7.jpg

Yes, that is the reverse light. I can't tell which wire you've tapped to, but there are only two. It is very easy to find out which is ground, ground is usually white and/or black color wire.

@TobiasSing Thanks! I tapped the red wire, but I'm having an issue. When I turn the car on, I immediately get a rearview feed. However, shouldn't I only get a feed when I put the car into reverse?

There's two possibilities, one, you have the running light and not the reverse light.

#2 Lexus could be turning on the reverse light by completing the circuit on the ground side of the reverse light circuit in order to turn it on, meaning that there will always be 12V going to the reverse light socket. Grab a multimeter to check for 12V constant at the bulb.

@morganc Thanks! I think that you might be right about option 2. As soon as I open the car door, and I haven't even turned on the car yet, I get a rearview feed. Strange.