An image processing device comprising: an obtaining unit configured to obtain a plurality of image data from an image capture device that moves along with a vehicle and of which image capture direction is a certain traveling direction of the vehicle; and a detection unit configured to detect features caused by reflections originating from an object inside of the vehicle based on positions of the features in an image corresponding to image data from among the plurality of image data, the image being captured while the vehicle has moved in a direction different from the image capture direction, wherein the detection unit is configured to: add a first value to appearance strengths at the positions of the features in a plurality of pieces of image data at a time when the vehicle has moved in the direction different from the image capture direction, subtract a second value from the appearance strengths at the positions of the features in the plurality of pieces of image data at a time when the vehicle has not moved in the direction different from the image capture direction and when the appearance strengths at the positions of the features are larger than a first threshold and the corresponding values of the features are smaller than a third threshold, and detect the feature caused by the reflection at a position at which the appearance strength is equal to or larger than a second threshold, wherein the appearance strengths depend on frequencies of appearances of the features in the plurality of image data, wherein the certain traveling direction is a forward direction of the vehicle, and wherein the different direction is a lateral direction. an obtaining unit configured to obtain a plurality of image data from an image capture device that moves along with a vehicle and of which image capture direction is a certain traveling direction of the vehicle; and a detection unit configured to detect features caused by reflections originating from an object inside of the vehicle based on positions of the features in an image corresponding to image data from among the plurality of image data, the image being captured while the vehicle has moved in a direction different from the image capture direction, wherein the detection unit is configured to: add a first value to appearance strengths at the positions of the features in a plurality of pieces of image data at a time when the vehicle has moved in the direction different from the image capture direction, subtract a second value from the appearance strengths at the positions of the features in the plurality of pieces of image data at a time when the vehicle has not moved in the direction different from the image capture direction and when the appearance strengths at the positions of the features are larger than a first threshold and the corresponding values of the features are smaller than a third threshold, and detect the feature caused by the reflection at a position at which the appearance strength is equal to or larger than a second threshold, add a first value to appearance strengths at the positions of the features in a plurality of pieces of image data at a time when the vehicle has moved in the direction different from the image capture direction, subtract a second value from the appearance strengths at the positions of the features in the plurality of pieces of image data at a time when the vehicle has not moved in the direction different from the image capture direction and when the appearance strengths at the positions of the features are larger than a first threshold and the corresponding values of the features are smaller than a third threshold, and detect the feature caused by the reflection at a position at which the appearance strength is equal to or larger than a second threshold, wherein the appearance strengths depend on frequencies of appearances of the features in the plurality of image data, wherein the certain traveling direction is a forward direction of the vehicle, and wherein the different direction is a lateral direction.