That picture is complete and only missing the transducers, the four bits that live in the bumper. Those blobs on the ends of the leads plug into the transducers.
The blue wire is a test/calibration loop.
. Park the car with rear bumper 50cm from a wall.
. Check the blue wire loop is connected to itself, switch on the ignition but not the engine, select reverse and wait for between 10 and 100 seconds while it self calibrates “BEEEEEEE…P”.
. Switch off.
. Open the loop again and tape the ends to protect them from shorting to anything.
I soldered my + and - onto the tangs at the back of the reverse-light socket, no wires needed cutting etc.
See my installation