We used Sloth to label our ground truth, please read instructions from https://sloth.readthedocs.io/en/latest/ 
and clone from https://github.com/cvhciKIT/sloth
1. Please use our custimized configuration file: 'config_clasp.py' ,typing in the terminal as: sloth --config config_clasp.py
   you can import images from your folder, after labeling, it will save your labels in a .json file