1. A method for searching image data representing an image from a database by using a query image, comprising: obtaining a query image data representing the query image; extracting information indicative of a shape of a contour of the query image and a shape of a skeleton of the query image, the contour constituting an outer edge of the query image, and the skeleton being located at the greatest distance from and inside the outer edge of the query image; counting a first number of pixels constituting the contour; counting a second number of pixels constituting the skeleton; comparing the ratio of the first number to the second number and a threshold number, the threshold number being determined to indicate that the first number is greater than twice the second number; determining that the query image is a closed region type when the ratio of the first number to the second number is less than the predetermined threshold number; determining that the query image is of an opened region type when the ratio of the first number to the second number is equal to or greater than the threshold number; reading out the image data of the closed region type from the database when the query image is determined to be of closed region type; reading out the image data of the opened region type from the database when the query image is determined to be of open region type; and determining the image data similar to the query image among the read out images.