oai-pmh.md

@@ -45,7 +45,7 @@ As mentioned above, some implementaion are returning content-type as _text/xml_
 ## Preferred optional Elements
 - **Descripton** - lom.general.description
 ## Optional Elements
-- **Thumbnail** - t.b.d
+- **Thumbnail** - lom.technical.thumbnail
 
 ## Custom LOM Elements
 ### centity