Raise ValueError for zero or negative sizes in ImageOps contain/cover/pad/fit

Tests/test_imageops.py

@@ -128,6 +128,18 @@ def test_contain_round() -> None:
     assert new_im.height == 5
 
 
+@pytest.mark.parametrize(
+    "operation", (ImageOps.contain, ImageOps.cover, ImageOps.pad, ImageOps.fit)
+)
+@pytest.mark.parametrize("size", ((0, 10), (10, 0), (-1, 10), (10, -1)))
+def test_size_must_be_positive(operation, size: tuple[int, int]) -> None:
+    # A zero or negative dimension must raise a clear ValueError, not a
+    # ZeroDivisionError (or silently return a wrong-sized image).
+    with Image.new("RGB", (100, 50)) as im:
+        with pytest.raises(ValueError, match="height and width must be > 0"):
+            operation(im, size)
+
+
 @pytest.mark.parametrize(
     "image_name, expected_size",
     (

docs/releasenotes/13.0.0.rst

@@ -101,3 +101,12 @@ to help projects prepare for 3.15, and to ensure Pillow could be used
 immediately at the release of 3.15.0 final (2026-10-01, :pep:`790`).
 
 Pillow 13.0.0 now officially supports Python 3.15.
+
+ImageOps invalid sizes
+^^^^^^^^^^^^^^^^^^^^^^^
+
+:py:meth:`~PIL.ImageOps.contain`, :py:meth:`~PIL.ImageOps.cover`,
+:py:meth:`~PIL.ImageOps.pad` and :py:meth:`~PIL.ImageOps.fit` now raise a
+``ValueError`` when the requested size has a dimension that is zero or negative.
+Previously a zero height raised ``ZeroDivisionError``, and some invalid sizes
+returned an incorrectly sized image.

src/PIL/ImageOps.py

@@ -277,6 +277,12 @@ def colorize(
     return _lut(image, red + green + blue)
 
 
+def _check_size(size: tuple[int, int]) -> None:
+    if size[0] <= 0 or size[1] <= 0:
+        msg = "height and width must be > 0"
+        raise ValueError(msg)
+
+
 def contain(
     image: Image.Image, size: tuple[int, int], method: int = Image.Resampling.BICUBIC
 ) -> Image.Image:
@@ -293,6 +299,8 @@ def contain(
     :return: An image.
     """
 
+    _check_size(size)
+
     im_ratio = image.width / image.height
     dest_ratio = size[0] / size[1]
 
@@ -324,6 +332,8 @@ def cover(
     :return: An image.
     """
 
+    _check_size(size)
+
     im_ratio = image.width / image.height
     dest_ratio = size[0] / size[1]
 
@@ -562,6 +572,8 @@ def fit(
     :return: An image.
     """
 
+    _check_size(size)
+
     # by Kevin Cazabon, Feb 17/2000
     # kevin@cazabon.com
     # https://www.cazabon.com