To dig deeper, there are couple of interesting nuances there:
- extreme number of objects on single photo, typical number of visible pieces in large pile is 1500-2000
- extreme number of classes in multi-class classification, there are ~1000 most common Lego bricks and up to 30000 classes if you include rare bricks and different patterns
- really hard data labelling: one photo can take up to a 5 work days to label