Determining object pose from image data

Systems and methods for determining pose using a trained neural network are described, whereby a user device receives image data of a 3-dimensional ("3D") marker affixed to a 3D object to be tracked, provides a set of input data derived from the image data to a neural network stored on the user device, and generates a pose descriptor indicative of estimated pose of the 3D marker based on output of the neural network produced in response to receiving the set of input data. The 3D marker comprises a first surface to convey radiation in a first direction, and a second surface to convey radiation in a second direction different to the first direction, whereby the image processing system determines object pose from captured image data of at least a portion of the radiation conveyed from the first and/or second surface of the 3D marker affixed to the 3D object.