If you'd like to have the same customised logo for all the webs, make these changes in [[TWikiPreferences]] instead of each web's WebPreferences, e.g.,
-- `Set WEBLOGOIMG = %PUBURLPATH%/TWiki/WebPreferences/mylogo.gif`
+- `Set WEBLOGOIMG = %PUBURLPATH%/Main/WebPreferences/mylogo.gif`
----