Hi James,
For Search Box MVC widget, sitefinity has BackgroundHint setting (SearchBoxBackgroundHint image). For old widget, SF doesnt have this setting, you can do that by modifying template of search box. You can do that on this way:
1) Save this code as SearchBox.ascx
<%@ Control Language=
"C#"
%>
<%@ Register TagPrefix=
"sitefinity"
Assembly=
"Telerik.Sitefinity"
Namespace=
"Telerik.Sitefinity.Web.UI"
%>
<sitefinity:ResourceLinks id=
"resourcesLinks"
runat=
"server"
UseEmbeddedThemes=
"True"
UseBackendTheme=
"True"
>
<sitefinity:ResourceFile JavaScriptLibrary=
"JQuery"
/>
<sitefinity:ResourceFile JavaScriptLibrary=
"KendoAll"
/>
<%-- <sitefinity:ResourceFile Name=
"Telerik.Sitefinity.Resources.Scripts.Kendo.styles.kendo_common_min.css"
Static=
"true"
/>
<sitefinity:ResourceFile Name=
"Telerik.Sitefinity.Resources.Scripts.Kendo.styles.kendo_default_min.css"
Static=
"true"
/>
<sitefinity:ResourceFile Name=
"Telerik.Sitefinity.Resources.Scripts.Kendo.styles.kendo_mobile_all_min.css"
Static=
"true"
/>--%>
</sitefinity:ResourceLinks>
<fieldset id=
"main"
class
=
"sfsearchBox"
runat=
"server"
>
<asp:TextBox ID=
"searchTextBox"
runat=
"server"
CssClass=
"sfsearchTxt"
/>
<asp:Button id=
"searchButton"
runat=
"server"
Text=
"<%$Resources:SearchResources, Search %>"
OnClientClick=
"return false;"
CssClass=
"sfsearchSubmit"
/>
</fieldset>
2) Place it inside of your project
3) Edit this template and put any placeholder
4) Go to widget settings of "Search Box" widget and change LayoutTemplatePath to the new path