How to customize and brand SharePoint 2010 Search Box?
Excellent post from Chris Stahl speaks about how you can customize and brand SharePoint 2010 search box. You can get source code and images to brand your search box for SharePoint 2010
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You can check this article also
http://www.sharepointdotnet.com/2012/02/branding-search-box-in-sharepoint-2010.html