1. https://www.gcc.tu-darmstadt.de/home/proj/dpid/index.en.jsp.
2. http://www.shengfenghe.com/publications/.
3. http://sipi.usc.edu/database/.
4. https://www2.eecs.berkeley.edu/Research/Projects/CS/vision/bsds/.
5. https://www.nasa.gov/multimedia/imagegallery/index.html.