I don't have an X-ray to show you, but in flagrant cases the frontal film of the chest, with contrast material to opacify the aorta, will show a distinct shape like a numeral 3, the indentation is that sharp. It can occur anywhere in the upper aorta but is most common at the descending aorta, where the Ductus Arteriosus arises. The ductus sends blood around the lungs while the baby is in the uterus and getting its oxygen from the placenta instead, and it's supposed to shrink down within hours of birth - but on rare occasions the adjacent aorta constricts too, and the child is left with a coarctation.

Clinically, milder cases "just" have high blood pressure, because the pinched-off aorta doesn't permit blood to get to the kidneys at the proper pressure, and they react by trying to get the pressure up. When it's high enough to satisfy the kidneys beyond the constriction, it's generally too high in the head and arms in front of it.

Lesser degrees of coarction can present (we've discussed that word before! It means "be detectable" or "show up") as lower BP in the legs compared to the arms, or as a "heart murmur," although the sound is made not by the heart but by a high-velocity jet of blood squirting through the narrowed aorta.

The illustration you show is an Echocardiogram, and shows the internal structures of the heart and great vessels rather than just their shadow, as a chest X-ray would. Truly a marvel of technology, the echocardiogram, clever in conception and absolutely elegant in implementation. But that's another story. Which I don't have the technical expertise to do justice to, so I'll just express my admiration of the engineering involved...