We first thank all the reviewers for their valuable comments and feedback. We owe our gratitude to Mr. Dan Fleming for his creative work which inspired our research and for his generosity in allowing us to use images of his works in this paper. Thanks also go to Daniel Cohen-Or and Nicholas Vining for proofreading, as well as to students from Hengyang Normal University and Dalian University of Technology for their hard work on data collection and labeling. This work is supported in part by grants from NSERC Canada, the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 61502153), the National Natural Science Foundation of China (Grant No. 61363048), and the Program of Key Disciplines in Hunan Province.