Do not send origin ContentType

processing_handler.go

@@ -162,7 +162,7 @@ func respondWithImage(reqID string, r *http.Request, rw http.ResponseWriter, sta
 		originURL,
 		po.Filename,
 		resultData.Format().Ext(),
-		originHeaders.Get(httpheaders.ContentType),
+		"",
 		po.ReturnAttachment,
 	)