This is an application to evaluate the similarity of images of the sky. It is based on three preprocessed indices: First, a vertical contour detection spanning the entire height of the image. It evaluates each pixel's probability to be on a horizon line. Second, a measure of local contrast to differentiate calm from turbulent weather conditions. Finally the average visual temperature of the image calculated from Hue values, normalised depending on the perception of different brightness and saturation levels. The application is designed to minimize the information processed in the comparison of two images at the cost of longer preprocessing, increasing computational efficiency when comparing a large number of images. Made with processing