Remove white square around a png image

I have a png image of a pin. I add it as a subview onto another imageview. But when I add it I see a white square around the pin itself. How can I remove that white background. I can see that white square when I view the file in Preview application. P.S. The platform is Mac OS X Snow Leopard. I开发者_Go百科'm developing an app for iPhone.I downloaded a png image from internet.

open that image with photoshop then select layers and then u will see two layer one for your pin other for backgroundlayer.right click then delete backgroundlayer then save again.ur problem solved.

do with Layer window pan in photoshop