How to join all image to one image

[Pavita]

hi,all

i have a new problem. :-D

i try to join all image to one image, now i can write macro that open  
image, specify pixel to paste image to new image.
but i confuse about region that overlap between image. new image will  
instead of old image or not? How to union or intersect in overlap  
region?

Regard,
Pavita