Update Sharepoint Site Logo through Powershell

Add-PSSnapin Microsoft.SharePoint.PowerShell

# get your site

$myApp = Get-SPWeb "http://server:port"

# add an logo image

$myApp.SuiteBarBrandingElementHtml = '<SharePoint:SPLinkButton CssClass="ms-siteicon-a"  runat="server" NavigateUrl="http://server:port" id="onetidProjectPropertyTitleGraphic"><SharePoint:SiteLogoImage CssClass="ms-siteicon-img" name="onetidHeadbnnr0"  id="onetidHeadbnnr2" LogoImageUrl="http://server:port/sites/Subsite/small- logo.png.png?rev=23" runat="server" href=""/></SharePoint:SPLinkButton>'

# update

$myApp.Update()