personal Google CG recaptured CG Figure 1:  Examples from our image sets.   Note the photorealism of all images. (a) Computer Graphics Architecture (295) Game (41) Nature (181) Object (220) Life (50) Hybrid (13) Indoor-light (40) Indoor-dark (38) Outdoor-rain (63)   Outdoor-night (26) Outdoor-day (76)   Outdoor-dusk (29) Natural-obj (62) Artificial-obj (66) (b) Author’s Personal Figure 2: (a) Subcategories within the  PRCG  image set and (b) Subcate- gories within Personal  image set, the number is the image count. 3   A Overview of the Columbia Photographic Im- ages and Photorealistic Computer Graphics Dataset We have designed and implemented the Columbia Photographic Images and Photorealistic Computer Graphics Dataset in accordance to the criteria men- tioned in Section 2. The dataset is used in our work for the classification of PIM and PRCG [21]. The dataset consists of four sets of images, as shown in Figure 1 and briefly described below. A detailed description would be given in the subsequent sections. 1.  800 PRCG images from the Internet (PRCG): These images are categorized by content into architecture, game, nature, object and life, see Figure 2(a).  The PRCG are mainly collected from 40 3D-graphics websites, such as www.softimage.com, www.3ddart.org, www.3d-ring.com  and so on. The rendering software used are such as 3ds MAX, softimage-xsi, Maya, Terragen and so on. The geometry modelling tools used include AutoCAD, Rhinoceros, softimage-3D and so on. The high-end rendering techniques used include global illumi- nation with ray tracing or radiosity, simulation of the camera depth-of- 5