Masking an image

Hello everybody,
I have an image with transparent background inside my picturebox on a winform.
I would really like to make the picturebox respond to click events only when the user clicks inside the picture. Nothing should happen if he clicks the background instead. How to do this?

Thanks in advance.
bye

Maybe look into regions in the GDI+ stuff.

thanks, I found a very interesting how-to about regions here
http://www.bobpowell.net/manipulate_graphics.htm
I think I'm happy ^^

Time for another topic, though