Rotary kilns are widely used in industry to achieve effective gas-solid heat transfer at high temperatures by direct contact with hot flue gases obtained by combustion. However, various disturbances related to nonpremixed combustion often used in practice introduces undesired variability in product quality and forces overheating, especially when obtaining the desired quality is dependent upon reaching a minimal solids discharge temperature. This paper investigates the use of digital RGB flame images and multivariate image analysis (MIA) techniques to quantify these combustion-related variations and to predict the future behavior of product quality. Very good solids discharge temperature forecasts were obtained over a time window running from current time t to about the mean residence time within the kiln using only a single flame image collected at time t. This information will be used to develop innovative automatic flame image-based control schemes to improve quality control and reduce fuel consumption.