The books also say that if the antenna is vertical to groundplane the iamge
is in phase and reinforces the wave emitted by vertical.
If antenna is horizontal and close to ground plane, the image cancels out
wave emitted by antenna.

Is this what happens in real life? It is known that if the 2 conductors of
twin feeder are close together, the fields cancel out and there is very
little radiation.

Are you saying that electromagnetic theory is wrong? What about fibre optic
cable? If ordinary glass strands were used, when the cable was bent, the
light would be blocked and not travel any further.