Question

so wonder is it need to be the same picture?

it can use difference picture ?

Answer 1

(Edited)
In link text stated:

When you submit your application, you
must include a 512 x 512 pixel version
of your application icon for display
in the App Store. Although it’s
important that this version be
instantly recognizable as your
application icon, it should be subtly
richer and more detailed. In other
words, you should not simply scale up
your application icon to create an
icon for the App Store.

So I think from this follows that you can make cosmetic changes to your picture to make it look better in good resolution.
In our app we do the reverse thing – we create 512×512 artwork and use its scaled to 57×57 variant as application icon.