PNG Images Don't Show Up Transparent

I posted a PNG image to my website header and that works fine and shows up as a transparent background. But when I posted to one of my pages the PNG images show up with a white background rather than transparent. Here is the page link: http://www.vancouverphotoworks.com/contact-4/contact-details/ I'm trying to have the social networking buttons show up with transparent backgrounds so you can see the page's background behind them. Thanks in advance for your help!