The image aesthetic benchmark [18] consists of 10800 Flickr photos of four categories, i.e., “animals”, “urban”, “people” and “nature”, and is constructed originally to retrieve beautiful yet unpopular images in social networks. The ground truths of the photos in the benchmark are five aesthetic grades: “Unacceptable” - images with extremely low quality, out of focus or underexposed, “Flawed” - images with some technical flaws and without any artistic value, “Ordinary” - standard quality images without technical flaws, “Professional” - professional-quality images with some artistic value, and “Exceptional” - very appealing images showing both outstanding professional quality and high artistic value.