Cut an image in irregular form

I need to create some images and use this images with dreamweaver and interact with this images with mouse click.

Some image are superimposed to another. For some reason if I click the image that is over another the one that is under reacts the mouse click.

Is it possible with Photoshop or Adobe Illustrator, for example, to cut out the image in a form that is not square or rectangular but irregular form?  This would solve my problem

Thanks.