Story 2125: Is RPI A Useful Measure? Published: 3/7/2008   Royalty free shooter Don Farrall argues that return-per-image (RPI) as I have calculated it has weaknesses as a measure of success. Companies offering stock images for sale need to continually provide customers with new material and a greater “depth of choice.” But as growth in number of images exceeds growth in revenue, RPI automatically falls. The problem is that older images in the count have less chance of selling and that skews the averages.