Well there are many ways of doing selection in Photoshop.
1. Using Magic Wand tool(experiment with tolerance values) (Select the white background 1st apply, smoothen selection then delete it)
2. Using Background Eraser
3. Using Extract filter(good for hair removal)
4. Using Pen tool(creating paths)
5. Selecting using QuickMask mode(best but time consuming)
6. Using Select>Color Range Option
You can extract the object/person easily if the background is plain like the 1st and 2nd pic. 3rd pic has many different colors and shades in the background.
Read this article about removing the background:
http://graphicssoft.about.com/od/pho...lrbps_1jet.htm