Visibility of a description on a description field hidden by a presenter is to be ensured while maintaining a positional relationship between the presenter and the description on the description field.The moving image data obtained by imaging a state where the presenter is giving the description onto the description field is processed to determine the description portion. Display data for displaying each of portions determined to be the description portion as a description is generated and superimposed on moving image data. For example, a difference value for each of pixels between a current frame image and a reference frame image is extracted, a group including a series of consecutive pixels having a difference value being a threshold or more is grasped and then, whether or not the group is a description portion is determined for each of the groups.