intermedia automatically update..

hi,
i am using Oracle 9i intermedia to manage an image database. I have created my table with ORDImage and ORDImage.Signature columns... . When i insert images then i use GenerateSignature to create their signatures in order to achieve content-based retrieval. But each time i insert a new image i have to create its signature...is there a way to make it happen automatically?? I am new to programming and i can t think of something...so your help would be really important to me..
thnx!!