Hitch angle detection system, hitch angle detection device, and non-transitory recording medium

A hitch angle detection system including:

• a trailer;
• a vehicle towing the trailer;
• a camera mounted on the vehicle;
• a hitch angle detection device detecting a hitch angle of the trailer based on an image of the trailer shot by the camera mounted on the vehicle by using a model obtained by performing learning using learning data which is a data set of the image of a learning trailer shot by a learning camera mounted on a learning vehicle and a label indicating the hitch angle of the learning trailer;
• and
• a server performing additional learning of the model, wherein
• the vehicle includes HMI accepting input of the hitch angle of the trailer used for the additional learning of the model and communication device communicating with the server,
• the camera mounted on the vehicle shoots an additional learning image of the trailer used for the additional learning of the model,
• the HMI accepts the input of the hitch angle of the trailer when the additional learning image of the trailer is shot,
• the server performs the additional learning of the model by using additional learning data which is the data set of the additional learning image of the trailer and the label indicating the hitch angle of the trailer, the input of the hitch angle of the trailer is accepted by the HMI,
• the hitch angle detection device detects the hitch angle of the trailer based on the image of the trailer shot by the camera mounted on the vehicle by using the model with the additional learning performed in the server.