Use embedded file.

bt5/erp5_web/PortalTypeAllowedContentTypeTemplateItem/allowed_content_types.xml

 <allowed_content_type_list>
  <portal_type id="Web Page">
-  <item>File</item>
-  <item>Image</item>
+  <item>Embedded File</item>
  </portal_type>
  <portal_type id="Web Page Module">
   <item>Web Page</item>

bt5/erp5_web/bt/revision

-1072
+1073
\ No newline at end of file

bt5/erp5_web/bt/template_portal_type_allowed_content_type_list

 Web Page Module | Web Page
-Web Page | File
-Web Page | Image
+Web Page | Embedded File
 Web Section | File
 Web Section | Image
 Web Section | Role Definition