I've read a bit about Kirlean photography in the past. What seems to have the most effect on the "aura" is the amount of moisture in the object. For example, I've read of studies where seeds with a good "aura" produced healthier plants than seeds with a dim "aura". However, other measurements also showed that the seeds with a bright "aura" contained more moisture than seeds with a dim "aura". Likewise, there were claims that you could tear a piece of a leaf away and sometimes still see the "aura" of the entire leaf. What was happening, though, was that the whole leaf, which had been previously tested, had left a residue on the apparatus, which then showed up in subsequent Kirlean photographs.
That's not to say that Kirlean photography is not valid for diagnostic purposes. Illnesses probably do cause various subtle biological changes that can affect moisture. Kirlean photography may be a practical way to measure these changes, but I doubt it is showing anything non-physical such as an "aura".
elphologist