Crashes in a threaded video streamer using NumPy and PyQt6 often stem from how QImage interacts with NumPy array memory. When a QImage is created from a NumPy array, it doesn't copy the data but instead references the original memory buffer. This creates a dangerous situation in multithreaded applications because if the worker thread modifies or discards the NumPy array, the QImage in the GUI thread can become invalid, leading to crashes. The solution is to ensure the QImage has its own independent copy of the data. This is achieved by calling the .copy() method on the QImage. The timing of this copy is crucial; it must be performed before the QImage is passed from the worker thread to the GUI thread, typically before emitting it via a signal. Furthermore, all GUI updates, such as calling setPixmap, must exclusively occur on the main thread. Using signals and slots is the correct way for worker threads to communicate with the main thread for GUI updates. The provided example demonstrates this by creating a QImage from a NumPy array, immediately copying it, and then emitting the copied QImage via a signal. A slot on the main thread receives this safe QImage, converts it to a QPixmap, and updates the QLabel without causing crashes. By implementing these practices, reliable threaded video streaming with PyQt6 can be achieved.