During the analog years of photography, it was possible to photograph pictures taken in the Infrared part of the light spectrum. Quite often, it led to a images that were simultaneously eerie looking (for the shift in colors) and slightly blurred by a reduced quality/resolution. It was only a matter of buying an IR filter and some IR-sensitive film. Then, you had to experiment.
Today, in the Digital Age of the Pixel, infrared photo became a little more difficult because, while the digital photo sensor is by nature very sensitive to infrared light, this is counteracted by filter removing this sensitivity (most sensors as so sensitive that they would produce bizarre-looking pictures if left untamed). Now, this is even more true for DSLR cameras which are nearly systematically closed to Infrared light (mostly, the only solution is a conversion involving replacing parts in the SLR camera and a lot of trial and error).
However, the images may be worth the effort if you look at some pictures produced by patient photographers.
More amazing tree infrared pictures at http://surfwithberserk.com/infrared-trees.