How to constrain the object detection problem?

1. Which method is best for object detection?
2. Why is object detection so hard?

Which method is best for object detection?

– RetinaNet is currently one of the best methods for object detection in a number of different tasks. It can be used as a replacement for a single-shot detector for a multitude of tasks to achieve quick and accurate results for images.

Why is object detection so hard?

Visual object recognition is an extremely difficult computational problem. The core problem is that each object in the world can cast an infinite number of different 2-D images onto the retina as the object's position, pose, lighting, and background vary relative to the viewer (e.g., [1]).