info about graphic in scheme

[Claudio Gamberini <cgamberini@inwind.it>]

hi, I'm a student of computer science.
I'm going to develop a graphical interface in scheme but i have a problem,
i draw some Picture into a canvas and with the coordinate x y i would like 
to know the bitmap who is draw on. Example:

(send (send cnvCanvas get-dc) draw-bitmap (make-object bitmap% PictureName) 
10 10)

GetPicture: x y --> picture

GetPicture 10 10 ---> PictureName (or an unique identifier for this picture)

can you help me?

thanks