I am new to designing and had got work for creating a live wallpaper using some animation characters in movies like Rio,Finding Nemo etc. How can use the images of that i find in google for this purpose.And also what kind of copyright permission i need to get ?
Your client will have to negotiate rights with the copyright owners.
I would recommend not putting a lot of time into this project until the client is able to provide you with evidence that they're cleared this very important legal hurdle. The "fair use" doctrine is not going to apply to a product that's going to be sold, or in all likelihood, even made available as a free download (especially if it's ad-supported).
You should also consult a lawyer in your area to determine what your personal legal liability might be before you go ahead with this, in case it turned out your client didn't have the right to copy.