Open up yor photos, I use angelina Jolie as my photo. Then go to Photoshop's Save for Web command.
switch to the Eyedropper tool in the Save for Web's Toolbox,
Click on the background color you want to become transparent. i choose white with eyedropper tool
Then, just below the Color Table on the bottom right of the
dialog, click on the first icon, which creates transparency from your selected color , save the file and you're done.