When you're making an image with a drop-shadow or subtle shading toward the edges, you want to crop away as much white as you can, but you don't want to crop away any of your drop-shadow. Look at the images below and to the right. Eww!
Here's a way to be sure you don't crop too much, but that you do crop enough:
Take the Magic Wand tool and set its Tolerance to 0 in the Options Bar.
Click it in the white area outside your image.
Select > Inverse. (or Ctrl-Shift-I) This makes only the part that is NOT white selected.
Image > Crop.
This is how your image will look in Photoshop --->
And here's how these will display when put onto a webpage!
Cropping Tips: a Photoshop Tutorial
