Restore image position after an error in ImageSequence.all_frames()

Tests/test_imagesequence.py

@@ -110,3 +110,24 @@ def test_all_frames() -> None:
         for i, im_frame in enumerate(ims):
             im.seek(i)
             assert_image_equal(im.rotate(90), im_frame)
+
+
+def test_all_frames_restores_position_after_seek_error() -> None:
+    class CustomImage(Image.Image):
+        def seek(self, frame: int) -> None:
+            if frame == 3:
+                msg = "seek failed"
+                raise ValueError(msg)
+            self.__frame = frame
+            self.im = Image.core.new("1", (1, 1))
+
+        def tell(self) -> int:
+            return self.__frame
+
+    with CustomImage() as im:
+        im.seek(1)
+
+        with pytest.raises(ValueError, match="seek failed"):
+            ImageSequence.all_frames(im)
+
+        assert im.tell() == 1

docs/releasenotes/13.0.0.rst

@@ -135,6 +135,12 @@ immediately at the release of 3.15.0 final (2026-10-01, :pep:`790`).
 
 Pillow 13.0.0 now officially supports Python 3.15.
 
+Restore image position if ImageSequence.all_frames() fails
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If processing a frame in :py:func:`~PIL.ImageSequence.all_frames` raises an exception,
+the given image will now seek back to its original frame.
+
 Fixed ImageChops.offset() for 16-bit images
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

src/PIL/ImageSequence.py

@@ -82,8 +82,8 @@ def all_frames(
     ims = []
     for imSequence in im:
         current = imSequence.tell()
-
-        ims += [im_frame.copy() for im_frame in Iterator(imSequence)]
-
-        imSequence.seek(current)
+        try:
+            ims += [im_frame.copy() for im_frame in Iterator(imSequence)]
+        finally:
+            imSequence.seek(current)
     return [func(im) for im in ims] if func else ims