As of MATLAB R2018b, we unfortunately do not support the R-CNN detection with GPU Coder. Currently, we only support the function 'matchFeatures' from the Computer Vision System Toolbox, but not 'detect'. We are moving forward to integrate this capability in future releases.
As for alternatives, we think YOLO will be your best bet. Alexnet and Squeeze will identify objects on the screen, but it does not provide the coordinates of the object.
Potentially you can try something like theTraffic Sign Detection and Recognition example where a YOLO-like DNN is used to detect objects, and a 2nd DNN is used to identify the object.
You may refer to the links below for other deep learning/object detection features currently supported by GPU Coder:
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