How does a camera take a photo of energy? Dark or otherwise?
Well, since a camera responds to photons emitted or reflected from its target it can only take a picture of energy.
More seriously, the camera is taking pictures of distant galaxies to study the accelerating expansion of the universe. Either there is something causing the acceleration (now called dark energy, although no one has actually observed it and determined if it matter, energy or something else) or the generally accepted rules about how gravity works is wrong.
It's a bit like flying to the Sun, you won't get burned up if you go at night...