Is there a way to copy from a hidden sheet to a hidden dialog box?

This is what I am trying to do. When something is selected in a drop down
box, I want a picture on a hidden sheet copied and pasted to a dialog box,
then I want this dialog box (hidden from editing) to pop up(which i can do).
The dialog box I have no problem with, in fact i can even copy and paste
everything if the sheets aren't hidden. However, when you hide the sheets you
can't select them so how can you copy & paste from them?
Any help would be greatly appreciated, I have got some wonderful answeres in
this group before.