Only deprecate setting of TIFF image sizes

Tests/test_file_tiff.py

@@ -69,6 +69,14 @@ class TestFileTiff(PillowTestCase):
         self.assertEqual(str(e.exception),
                          "Not allowing setting of legacy api")
 
+    def test_size(self):
+        filename = "Tests/images/pil168.tif"
+        im = Image.open(filename)
+
+        def set_size():
+            im.size = (256, 256)
+        self.assert_warning(DeprecationWarning, set_size)
+
     def test_xyres_tiff(self):
         filename = "Tests/images/pil168.tif"
         im = Image.open(filename)

src/PIL/TiffImagePlugin.py

@@ -1049,6 +1049,19 @@ class TiffImageFile(ImageFile.ImageFile):
         "Return the current frame number"
         return self.__frame
 
+    @property
+    def size(self):
+        return self._size
+
+    @size.setter
+    def size(self, value):
+        warnings.warn(
+            'Setting the size of a TIFF image direcly is deprecated, and will '
+            'be removed in a future version. Use the resize method instead.',
+            DeprecationWarning
+        )
+        self._size = value
+
     def load(self):
         if self.use_load_libtiff:
             return self._load_libtiff()