Suggestions for Open-Source Tool for Image Classifications (with Nesting)

I'm looking for an open source tool to assist my colleagues and I to label images for a machine learning application. We don't actually need bounding boxes or anything to pinpoint regions within each image, and instead need solely global image classifications (e.g. whether the image is one of a cityscape, rural setting etc).

The mission-critical functionality we're looking for is:

• image classification (both radio boxes and checklists)
• the ability to nest labels, e.g. if label1=cityscape then label2 is required etc

Ideally it would also have one or more of the following features:

• managing users / assigning tasks etc
• the ability to provide labellers with a qualification test to measure their labelling vs pre-labelled images
• metrics such as time per label, total time etc
• the labelling UI to allow for available label options to be images or icons rather than text (e.g. rather than have text labels of 'square' or 'round', we actually show a square icon or round icon)