Command line is quicker. Install Imagemagick.
Put together a bash script file:
Run it and then you will be done. Note that the above will add transparency to everything that is white 'FFFFFF' including any pixels of that colour inside your image. "topLeftPixel" can be used instead of "white" for autodecting background colour.
If the white pixels in image problem is a problem then you can do Photoshop batch. Layer mask is better than 'delete'-clearing the white pixels as you do not actually alter the RGB layers.
If you use GIMP, I can suggest this tutorial: Perfect masking using a highpass guide. I had very good results with complex images by following it.
For the sake of completion i had to add one more method (if you using photoshop). As your image is not complex you can use the magic wand, or select color. But best method for separating a complex foreground from a relatively less complex background is Channel masking.
Here is a good tutorial which might be helpful for future visitors: http://graphics.tutremix.com/tutorials/photo-effect/how-to-make-a-lightning-man-photomanipulation-in-photoshop-day-1/
It depends on the software you have available to you.
If you have Photoshop, for an image that clean you can do it very quickly:
If you get a white halo around your image, try using menu