A safety device is disclosed for a gantry crane configured to lift containers from a truck driven chassis. The safety device estimates truck movement when the gantry crane lifts the container and sends an alert to avert lifting the truck when the container fails to decouple from the chassis. Motion sensors are disclosed that are configured to coupled to a trolley of a gantry crane and used to create an estimate of the front or back region near a container being lifted. A processor may use the motion sensor signals to avert lifting the truck and/or to avert an Optical Character Recognition (OCR) system reporting a container identification failure when a hatch cover is lifted off of a ship. In various embodiments, the processor may be included in the safety device and/or in the OCR system.
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