According to an embodiment, an object detection system includes an obtaining unit, an estimating unit, a setting unit, a calculating unit, and a detecting unit. The obtaining unit is configured to obtain an image in which an object is captured. The estimating unit is configured to estimate a condition of the object. The setting unit is configured to set, in the image, a plurality of areas that have at least one of a relative positional relationship altered according to the condition and a shape altered according to the condition. The calculating unit is configured to calculate a feature value of an image covering the areas. The detecting unit is configured to compare the calculated feature value with a feature value of a predetermined registered object, and detect the registered object corresponding to the object.