How do I change the screen with the slider on my itouch?

I have seen videos of people with things like the battery and other stuff that isn't on the wallpaper section on the screen that comes up when you press either the home button or top button. If you don't know what im talking about, its the one that says slide to unlock. Is it only possible to have the battery when charging or can i have it all the time?How do I change the screen with the slider on my itouch?
Those ipods are jailbroken.How do I change the screen with the slider on my itouch?
you can change it (it is called a wallpaper) by going into your pictures, select the one you want as a wallpaper, and press the little button at the bottom left corner.

select use as wallpaper