An image works as long as there is a center section in the vertical and/or the horizontal that is repeatable. The number of pixels in that center section will then determine the size increments that you can scale the image up. Say for example you have a 15 x 15 image that can be broken up into 9 - 5 x 5 pixel units. If 5 pixels are repeatable in the horizontal and vertical you could scale it up to 20 x 20, 25 x 25, 30 x 30, etc... But if you scaled it up to say 27 x 27 you would only get a partial repeat of the center 5 pixels and it would be obvious.
I don't know if that made any sense. If it didn't I'll make an example when I get off work.
As for an animation, you could use 9-patch as a background for the animation, but I think that is about it.