Getting Web Resources from the CRM 2011 Ribbon

If your creating a custom action/ribbon feature and you want to reference a file in your webresources, then adding the $websresource variable will allow for this.
e.g and image location could be

<Button
Id="B_TextButton"
LabelText="Send TXT"
ToolTipTitle="Send a TXT Message"
ToolTipDescription="Send a TXT message to this entity record, if the mobile number is provided"
TemplateAlias="o1"
Image16by16= "$webresource:new_txt16.png"
Image32by32="$webresource:new_txt32.png"/>


</CommandUIDefinition>