To remove the white (or any other color) from an image.

1) Create a transparent layer (same dimensions as image about to be edited)
2) Paste your image onto it.
3) Select > Color Range - A dropper will appear. Select the white you'd like to remove and click on it. (works for any other color you'd like to remove as well). Usually, you can keep the fuzziness to 40-50.
4) Click OK, and the selected color will be highlighted.
5) Press the delete key and the selected area (i.e. the selected color) will be removed, leaving very clean edges.