diff --git a/isc.py b/isc.py
index 101d4a7..af85702 100644
--- a/isc.py
+++ b/isc.py
@@ -69,10 +69,11 @@ class Isc(NNOperator):
         ])
 
     def __call__(self, data: Union[List[towhee._types.Image], towhee._types.Image]):
-        if not isinstance(data, list):
+        if isinstance(data, towhee._types.Image):
             imgs = [data]
         else:
             imgs = data
+
         img_list = []
         for img in imgs:
             img = self.convert_img(img)