#Image
I am not sure exactly the question you are asking, but generally for
manipulating any part of a gadget, you have to do a RemoveGadget() then the
work followed by an AddGadget(). Actually, I tend to use the GList version
of the routines because I am almost always dealing with more than one
gadget.
For an Image sturcture, I don't understand the comment about
constants/variables. You can declare an image structure as part of your
code and then point the image data pointer to some chip ram that you
allocate (or declare as __chip). I can provide an example if this is what
you are asking.