How To Hide Ribbon From Anonymous Users in Sharepoint 2010

1)      Open your SharePoint v4.master page in sharepoint designer

2)      Locate this line:

<div id="s4-ribbonrow">

3)      Change it to:

<div id="s4-ribbonrow" style="display:none">

4)      Now find the end of the “s4-ribbonrow” tag and add following block right after it:

<Sharepoint:SPSecurityTrimmedControl ID="SPSecurityTrimmedControl2" runat="server" PermissionsString="AddAndCustomizePages">
<script type="text/javascript">
document.getElementById("s4-ribbonrow").style.display = "block";
</script>
</Sharepoint:SPSecurityTrimmedControl>

5)      Save the v4.master page and publish it.