Their method is detailed in the whitepaper [1], mainly section 3.2. TL;DR mturk for high level annotations (frame contains/does not contain object in class), an

Their method is detailed in the whitepaper [1], mainly section 3.2. TL;DR mturk for high level annotations (frame contains/does not contain object in class), and internal annotators for bounding boxes. [1] https://arxiv.org/pdf/1702.00824.pdf https://arxiv.org/pdf/1702.00824.pdf