Ok, lemme try this out:
1) Open the picture you want to edit. Delete all the white around it, however you like to do that. I prefer to use the Magic Wand tool.
2) Do to the fact I have no clue what version of Photoshop you are using you'll have to mess around on your own to find this next part:
Towards the very bottom of the toolbar pallette there should be two buttons, each button has a circle in the middle, but one button has a black-ish background while the other is white. Select the one with the black background.
3) Now select your gradient tool, and change it's settings to be: white to transparent, and the circle gradient (the white circle fading into black backround).
4) Now start in the center of your image and drag to the corner of the image (not the canvas, just the actual image [ the head ] ). A red circle thingey should appear around the image now.
5) Now remember the two circle buttons I mentioned at the beginning? Click the one with the white background this time. And press delete.
That should do it! You might want to mess around a bit until you get it right. Sorry, I'm not too good when it comes to writing tutorials.