Google Open Image V5

Initially introduced in 2016 (v1), Google's Open Image has now been updated in 2019 with new segmentation masks and a focus around instance segmentation. Open Images V5 features segmentation masks for 2.8 million object instances in 350 categories. In addition to the masks, they also added 6.4M new human-verified image-level labels, reaching a total of 36.5M over nearly 20,000 categories. This dataset is highly suitable for building object detection models.

https://storage.googleapis.com/openimages/web/index.html