r/MachineLearning - [D] Inter-annotator agreement: how does it work for computer vision?

We have a dataset which we need to annotate: the task is object detection, thus we need to create bounding boxes. But I'mm open to alternative suggestions, if you think there are better tools. Since the dataset is very large and very confidential, we're going to annotate it in-house. I've heard of people trying to estimate the error due to subjectivity/mistakes in human annotation, but I don't quite understand how it works. Let's suppose for the sake of example that I have 900 images and 3 annotators.