References that answer the question you actually searched.

Keypoint annotation, done well

Defining a keypoint schema and skeleton, placing points, handling occlusion and left/right confusion, review workflows, and export formats.

The COCO keypoint format

All 17 keypoints in order, 0-based vs 1-based indexing, the official skeleton pairs, visibility flags, and worked annotation JSON.

Keypoint and pose estimation datasets

Downloadable keypoint datasets hosted on DataTorch, plus the standard benchmarks (COCO, MPII, CrowdPose, AP-10K and more) with sizes and keypoint counts.

The DSB2018 nuclei segmentation dataset

What is inside the standard nuclei benchmark, the per-nucleus mask format, common pitfalls, and which model to train: U-Net, StarDist, Cellpose, or Mask R-CNN.