Not a bad question, though a difficult concept to measure in reality. We can estimate the emissions caused by crypto-currency as that is almost entirely CPU-bo

Not a bad question, though a difficult concept to measure in reality. We can estimate the emissions caused by crypto-currency as that is almost entirely CPU-bound by about the same amount (or an easy to estimate average) per unit. The costs of transmission and storage are going to be relatively minor. For images the compression cost, while the process is similarly CPU-bound, is pretty small unless you are doing something small like compressing to hundreds/thousands of algorithm/parameter combinations and picking the best result (perhaps by some heuristic more complex than final file size). Also transmission and strorage costs are difficult to estimate because for any given image how do you guestimate how many times it will move and be copied? Having said that, the article's statement that: “[as] bandwidth savings from overly lossy image codecs will become meaningless, [] the CPU/user time and battery or grid energy spent on complex decompression steps will be wasted.” implies that energy use is at least a coincidental consideration here. Though image quality is by far the primary concern, and that despite being subjective is probably an easier metric to measure in this case, with compression time likely to be ahead of energy use too.