200 400 600 800 1000 1200 1400 1600 0 10 20 30 40 50 60 70 80 90 100 Averaged Dimension of Google Set Images Figure 7: The histogram of the average dimension of the Google  set. 6   The Google  Set The Google set is from the search results based on the keywords that matches the  PRCG  set.  The keywords are architecture, nature scene, landscape, animal, building, people, scenery, indoor, object, machine, insect, interior, plant, forest, vehicle, fruit and statue. The images are filtered subjectively to include only PIM of size larger than 300 pixels for the width or the height, whichever smaller. The size of the Google  images varies between 315 pixels and 1500 pixels in average dimension, (width + height)/2, with the mean at 660 pixels. Figure 7 shows the histogram of the average dimension of the Google set. 7   The Recaptured PRCG  Set The recaptured PRCG set consists of the photographed screen display of the 800 images from the PRCG set. PRCG are displayed on a 17-inch LCD mon- itor screen with a display resolution of 1280x1024 pixels and photographed by a Canon G3 digital camera mounted on a tripod at a distance of four feet in front of the screen. The captured images have a resolution 1024x768 pixels and of a high quality JPEG compression.  The camera operates at the time-priority mode where the shutter speed is set to 1/4 seconds while the aperture size and focal length are set automatic. The acquisition is con- ducted in a dark room in order to reduce the reflections from the ambient scene. 19