transparent picure boxes

[MyersGer]

hi

i got a problem with transparent zones in pictureboxes.
first of all:
i want to have a picturebox as background then i want to place other pboxes on it. these will have onclick methods.
it's a map where you can click the countries.

but when i place a pbox on the background pbox the square cover the background picture although the picture has transparent "borders"
and the picturebox backgrund color is set also to transparent.

has anyone an idea how i can make the pictureboxes transparent? or any suggestion how i can realize a map with clickable countries?

thx
myers