"How much does a digital image weigh?" A few months ago my colleague, Phil Gallagher, asked this hypothetical question in his magazine, le Boogie. The scientific answer, I guess, is nothing, or next to nothing, the small array of digital bits which compose an electronic file are barely measurable by scientific means.

But think of a good image, or take a look at these ones by Che Chorley. How is it that they can't be quantified? As electronic files they barely register, their dimensions and weight and imposition upon the physical world barely exists. Unseen from human eyes they also have no emotional bearing.

Yet once viewed, a digital image can conjure many feelings - it can stir excitement and it can convey mystery. It can provoke memory. The emotional content creates a response that is palpable. And that, I believe, is how you measure a good image.

Images from the outback taken by Che Chorley.//STUART NETTLE