Examples of rare image artifacts. Left: Image r418779, CCD#4. The left and right edges show a 5% difference in background counts. Right: Image r531376, CCD#4. The feature, top right, causes up to a 10% difference relative to the background. The HAGRID superpixel map is shown to enhance low level detail. Black areas correspond to rejected superpixels due to high levels of masking. The colour scale goes from red (low values) to blue (high values).