1. An object determining device comprising at least one processor which implements: an imager for obtaining an image of the object; a likelihood value calculator for calculating a first likelihood value for the object shown in the image obtained by the imager by use of the image obtained by the imager and a machine learning system trained so as to respond to a sample image of a sample object that is wearing a covering, the sample image of the sample object that is wearing the covering is applied with a first teacher signal 1 as a first excitatory information and the sample image of the sample object that is not wearing the covering is applied with a first teacher signal 0 as a first inhibitor information, and for calculating a second likelihood value for the object shown in the image obtained by the imager by use of the image obtained by the imager and a machine learning system trained so as to respond to a sample image of a sample object that is not wearing a covering, the sample image of the sample object that is not wearing the covering is applied with a second teacher signal 1 as a second excitatory information and the sample image of the sample object that is wearing the covering is applied with a second teacher signal 0 as a second inhibitor information, the first likelihood value indicating a level of likelihood that the object is wearing the covering and the second likelihood value indicating a level of likelihood that the object is not wearing the covering; and a determiner for determining whether or not the object, shown in the image obtained by the imager, is wearing a covering, on the basis of a ratio between the first likelihood value and the second likelihood value calculated by the likelihood value calculator.