diff --git a/tools/infer.py b/tools/infer.py
index 89591080d21137197589e2a5ab42b64f58c0dee9..3835264b2099562e4dfcb3accf07ebf02119b886 100644
--- a/tools/infer.py
+++ b/tools/infer.py
@@ -74,20 +74,20 @@ def get_test_images(infer_dir, infer_img):
             "{} is not a file".format(infer_img)
     assert infer_dir is None or os.path.isdir(infer_dir), \
             "{} is not a directory".format(infer_dir)
-    images = []
 
     # infer_img has a higher priority
     if infer_img and os.path.isfile(infer_img):
-        images.append(infer_img)
-        return images
+        return [infer_img]
 
+    images = set()
     infer_dir = os.path.abspath(infer_dir)
     assert os.path.isdir(infer_dir), \
         "infer_dir {} is not a directory".format(infer_dir)
     exts = ['jpg', 'jpeg', 'png', 'bmp']
     exts += [ext.upper() for ext in exts]
     for ext in exts:
-        images.extend(glob.glob('{}/*.{}'.format(infer_dir, ext)))
+        images.update(glob.glob('{}/*.{}'.format(infer_dir, ext)))
+    images = list(images)
 
     assert len(images) > 0, "no image found in {}".format(infer_dir)
     logger.info("Found {} inference images in total.".format(len(images)))