diff --git a/src/PIL/BmpImagePlugin.py b/src/PIL/BmpImagePlugin.py
index c5d1cd40d3b..2df1d8d33bd 100644
--- a/src/PIL/BmpImagePlugin.py
+++ b/src/PIL/BmpImagePlugin.py
@@ -25,6 +25,7 @@
 from __future__ import annotations
 
 import os
+from typing import IO
 
 from . import Image, ImageFile, ImagePalette
 from ._binary import i16le as i16
@@ -52,7 +53,7 @@ def _accept(prefix: bytes) -> bool:
     return prefix[:2] == b"BM"
 
 
-def _dib_accept(prefix):
+def _dib_accept(prefix: bytes) -> bool:
     return i32(prefix) in [12, 40, 52, 56, 64, 108, 124]
 
 
@@ -394,11 +395,13 @@ def _open(self) -> None:
 }
 
 
-def _dib_save(im, fp, filename):
+def _dib_save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
     _save(im, fp, filename, False)
 
 
-def _save(im, fp, filename, bitmap_header=True):
+def _save(
+    im: Image.Image, fp: IO[bytes], filename: str, bitmap_header: bool = True
+) -> None:
     try:
         rawmode, bits, colors = SAVE[im.mode]
     except KeyError as e:
diff --git a/src/PIL/BufrStubImagePlugin.py b/src/PIL/BufrStubImagePlugin.py
index 826e89dafea..6f52204b829 100644
--- a/src/PIL/BufrStubImagePlugin.py
+++ b/src/PIL/BufrStubImagePlugin.py
@@ -10,6 +10,8 @@
 #
 from __future__ import annotations
 
+from typing import IO
+
 from . import Image, ImageFile
 
 _handler = None
@@ -58,7 +60,7 @@ def _load(self) -> ImageFile.StubHandler | None:
         return _handler
 
 
-def _save(im, fp, filename):
+def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
     if _handler is None or not hasattr(_handler, "save"):
         msg = "BUFR save handler not installed"
         raise OSError(msg)
diff --git a/src/PIL/DdsImagePlugin.py b/src/PIL/DdsImagePlugin.py
index 1575f2d88b6..a3efadb030d 100644
--- a/src/PIL/DdsImagePlugin.py
+++ b/src/PIL/DdsImagePlugin.py
@@ -16,6 +16,7 @@
 import struct
 import sys
 from enum import IntEnum, IntFlag
+from typing import IO
 
 from . import Image, ImageFile, ImagePalette
 from ._binary import i32le as i32
@@ -510,7 +511,7 @@ def decode(self, buffer):
         return -1, 0
 
 
-def _save(im, fp, filename):
+def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
     if im.mode not in ("RGB", "RGBA", "L", "LA"):
         msg = f"cannot write mode {im.mode} as DDS"
         raise OSError(msg)
diff --git a/src/PIL/GifImagePlugin.py b/src/PIL/GifImagePlugin.py
index 962a9283464..e62852db31d 100644
--- a/src/PIL/GifImagePlugin.py
+++ b/src/PIL/GifImagePlugin.py
@@ -31,6 +31,7 @@
 import subprocess
 from enum import IntEnum
 from functools import cached_property
+from typing import IO
 
 from . import (
     Image,
@@ -336,14 +337,13 @@ def _seek(self, frame, update_image=True):
                         self._mode = "RGB"
                         self.im = self.im.convert("RGB", Image.Dither.FLOYDSTEINBERG)
 
-        def _rgb(color):
+        def _rgb(color: int) -> tuple[int, int, int]:
             if self._frame_palette:
                 if color * 3 + 3 > len(self._frame_palette.palette):
                     color = 0
-                color = tuple(self._frame_palette.palette[color * 3 : color * 3 + 3])
+                return tuple(self._frame_palette.palette[color * 3 : color * 3 + 3])
             else:
-                color = (color, color, color)
-            return color
+                return (color, color, color)
 
         self.dispose_extent = frame_dispose_extent
         try:
@@ -709,11 +709,13 @@ def _write_multiple_frames(im, fp, palette):
     return True
 
 
-def _save_all(im, fp, filename):
+def _save_all(im: Image.Image, fp: IO[bytes], filename: str) -> None:
     _save(im, fp, filename, save_all=True)
 
 
-def _save(im, fp, filename, save_all=False):
+def _save(
+    im: Image.Image, fp: IO[bytes], filename: str, save_all: bool = False
+) -> None:
     # header
     if "palette" in im.encoderinfo or "palette" in im.info:
         palette = im.encoderinfo.get("palette", im.info.get("palette"))
@@ -730,7 +732,7 @@ def _save(im, fp, filename, save_all=False):
         fp.flush()
 
 
-def get_interlace(im):
+def get_interlace(im: Image.Image) -> int:
     interlace = im.encoderinfo.get("interlace", 1)
 
     # workaround for @PIL153
diff --git a/src/PIL/GribStubImagePlugin.py b/src/PIL/GribStubImagePlugin.py
index c27cffab63e..b24dcded2f9 100644
--- a/src/PIL/GribStubImagePlugin.py
+++ b/src/PIL/GribStubImagePlugin.py
@@ -10,6 +10,8 @@
 #
 from __future__ import annotations
 
+from typing import IO
+
 from . import Image, ImageFile
 
 _handler = None
@@ -58,7 +60,7 @@ def _load(self) -> ImageFile.StubHandler | None:
         return _handler
 
 
-def _save(im, fp, filename):
+def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
     if _handler is None or not hasattr(_handler, "save"):
         msg = "GRIB save handler not installed"
         raise OSError(msg)
diff --git a/src/PIL/IcoImagePlugin.py b/src/PIL/IcoImagePlugin.py
index cea093f9c6c..af94e5a2e7f 100644
--- a/src/PIL/IcoImagePlugin.py
+++ b/src/PIL/IcoImagePlugin.py
@@ -25,6 +25,7 @@
 import warnings
 from io import BytesIO
 from math import ceil, log
+from typing import IO
 
 from . import BmpImagePlugin, Image, ImageFile, PngImagePlugin
 from ._binary import i16le as i16
@@ -39,7 +40,7 @@
 _MAGIC = b"\0\0\1\0"
 
 
-def _save(im, fp, filename):
+def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
     fp.write(_MAGIC)  # (2+2)
     bmp = im.encoderinfo.get("bitmap_format") == "bmp"
     sizes = im.encoderinfo.get(
@@ -194,7 +195,7 @@ def getimage(self, size, bpp=False):
         """
         return self.frame(self.getentryindex(size, bpp))
 
-    def frame(self, idx):
+    def frame(self, idx: int) -> Image.Image:
         """
         Get an image from frame idx
         """
@@ -205,6 +206,7 @@ def frame(self, idx):
         data = self.buf.read(8)
         self.buf.seek(header["offset"])
 
+        im: Image.Image
         if data[:8] == PngImagePlugin._MAGIC:
             # png frame
             im = PngImagePlugin.PngImageFile(self.buf)
diff --git a/src/PIL/ImImagePlugin.py b/src/PIL/ImImagePlugin.py
index 8e949ebaf9d..c98cfb0984b 100644
--- a/src/PIL/ImImagePlugin.py
+++ b/src/PIL/ImImagePlugin.py
@@ -28,6 +28,7 @@
 
 import os
 import re
+from typing import IO, Any
 
 from . import Image, ImageFile, ImagePalette
 
@@ -103,7 +104,7 @@
 split = re.compile(rb"^([A-Za-z][^:]*):[ \t]*(.*)[ \t]*$")
 
 
-def number(s):
+def number(s: Any) -> float:
     try:
         return int(s)
     except ValueError:
@@ -325,7 +326,7 @@ def tell(self) -> int:
 }
 
 
-def _save(im, fp, filename):
+def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
     try:
         image_type, rawmode = SAVE[im.mode]
     except KeyError as e:
diff --git a/src/PIL/Image.py b/src/PIL/Image.py
index 6385f204bf2..8cb4b7e3292 100644
--- a/src/PIL/Image.py
+++ b/src/PIL/Image.py
@@ -2875,7 +2875,7 @@ def transpose(self, method: Transpose) -> Image:
         self.load()
         return self._new(self.im.transpose(method))
 
-    def effect_spread(self, distance):
+    def effect_spread(self, distance: int) -> Image:
         """
         Randomly spread pixels in an image.
 
@@ -3012,7 +3012,7 @@ def new(
     return im._new(core.fill(mode, size, color))
 
 
-def frombytes(mode, size, data, decoder_name="raw", *args) -> Image:
+def frombytes(mode, size, data, decoder_name: str = "raw", *args) -> Image:
     """
     Creates a copy of an image memory from pixel data in a buffer.
 
@@ -3051,7 +3051,7 @@ def frombytes(mode, size, data, decoder_name="raw", *args) -> Image:
     return im
 
 
-def frombuffer(mode, size, data, decoder_name="raw", *args) -> Image:
+def frombuffer(mode: str, size, data, decoder_name: str = "raw", *args) -> Image:
     """
     Creates an image memory referencing pixel data in a byte buffer.
 
@@ -3553,7 +3553,7 @@ def register_save(id: str, driver) -> None:
     SAVE[id.upper()] = driver
 
 
-def register_save_all(id, driver) -> None:
+def register_save_all(id: str, driver) -> None:
     """
     Registers an image function to save all the frames
     of a multiframe format.  This function should not be
@@ -3565,7 +3565,7 @@ def register_save_all(id, driver) -> None:
     SAVE_ALL[id.upper()] = driver
 
 
-def register_extension(id, extension) -> None:
+def register_extension(id: str, extension: str) -> None:
     """
     Registers an image extension.  This function should not be
     used in application code.
@@ -3576,7 +3576,7 @@ def register_extension(id, extension) -> None:
     EXTENSION[extension.lower()] = id.upper()
 
 
-def register_extensions(id, extensions) -> None:
+def register_extensions(id: str, extensions: list[str]) -> None:
     """
     Registers image extensions.  This function should not be
     used in application code.
@@ -3588,7 +3588,7 @@ def register_extensions(id, extensions) -> None:
         register_extension(id, extension)
 
 
-def registered_extensions():
+def registered_extensions() -> dict[str, str]:
     """
     Returns a dictionary containing all file extensions belonging
     to registered plugins
@@ -3650,7 +3650,7 @@ def effect_mandelbrot(size, extent, quality):
     return Image()._new(core.effect_mandelbrot(size, extent, quality))
 
 
-def effect_noise(size, sigma):
+def effect_noise(size: tuple[int, int], sigma: float) -> Image:
     """
     Generate Gaussian noise centered around 128.
 
@@ -3661,7 +3661,7 @@ def effect_noise(size, sigma):
     return Image()._new(core.effect_noise(size, sigma))
 
 
-def linear_gradient(mode):
+def linear_gradient(mode: str) -> Image:
     """
     Generate 256x256 linear gradient from black to white, top to bottom.
 
@@ -3670,7 +3670,7 @@ def linear_gradient(mode):
     return Image()._new(core.linear_gradient(mode))
 
 
-def radial_gradient(mode):
+def radial_gradient(mode: str) -> Image:
     """
     Generate 256x256 radial gradient from black to white, centre to edge.
 
diff --git a/src/PIL/MpoImagePlugin.py b/src/PIL/MpoImagePlugin.py
index 766e1290ced..6716722f204 100644
--- a/src/PIL/MpoImagePlugin.py
+++ b/src/PIL/MpoImagePlugin.py
@@ -22,6 +22,7 @@
 import itertools
 import os
 import struct
+from typing import IO
 
 from . import (
     Image,
@@ -32,7 +33,7 @@
 from ._binary import o32le
 
 
-def _save(im, fp, filename):
+def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
     JpegImagePlugin._save(im, fp, filename)
 
 
diff --git a/src/PIL/PdfImagePlugin.py b/src/PIL/PdfImagePlugin.py
index 1777f1f20db..ccd28f3434b 100644
--- a/src/PIL/PdfImagePlugin.py
+++ b/src/PIL/PdfImagePlugin.py
@@ -25,6 +25,7 @@
 import math
 import os
 import time
+from typing import IO
 
 from . import Image, ImageFile, ImageSequence, PdfParser, __version__, features
 
@@ -39,7 +40,7 @@
 #  5. page contents
 
 
-def _save_all(im, fp, filename):
+def _save_all(im: Image.Image, fp: IO[bytes], filename: str) -> None:
     _save(im, fp, filename, save_all=True)
 
 
diff --git a/src/PIL/SpiderImagePlugin.py b/src/PIL/SpiderImagePlugin.py
index e5242395f92..98dd91c0e24 100644
--- a/src/PIL/SpiderImagePlugin.py
+++ b/src/PIL/SpiderImagePlugin.py
@@ -37,7 +37,7 @@
 import os
 import struct
 import sys
-from typing import TYPE_CHECKING
+from typing import IO, TYPE_CHECKING
 
 from . import Image, ImageFile
 
@@ -263,7 +263,7 @@ def makeSpiderHeader(im: Image.Image) -> list[bytes]:
     return [struct.pack("f", v) for v in hdr]
 
 
-def _save(im, fp, filename):
+def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
     if im.mode[0] != "F":
         im = im.convert("F")
 
@@ -279,7 +279,7 @@ def _save(im, fp, filename):
     ImageFile._save(im, fp, [("raw", (0, 0) + im.size, 0, (rawmode, 0, 1))])
 
 
-def _save_spider(im, fp, filename):
+def _save_spider(im: Image.Image, fp: IO[bytes], filename: str) -> None:
     # get the filename extension and register it with Image
     ext = os.path.splitext(filename)[1]
     Image.register_extension(SpiderImageFile.format, ext)
diff --git a/src/PIL/TiffImagePlugin.py b/src/PIL/TiffImagePlugin.py
index f3fa3c24ccd..04f36744bed 100644
--- a/src/PIL/TiffImagePlugin.py
+++ b/src/PIL/TiffImagePlugin.py
@@ -1995,7 +1995,7 @@ def newFrame(self) -> None:
         self.finalize()
         self.setup()
 
-    def __enter__(self):
+    def __enter__(self) -> AppendingTiffWriter:
         return self
 
     def __exit__(self, exc_type, exc_value, traceback):
@@ -2023,7 +2023,7 @@ def goToEnd(self) -> None:
             self.f.write(bytes(pad_bytes))
         self.offsetOfNewPage = self.f.tell()
 
-    def setEndian(self, endian):
+    def setEndian(self, endian: str) -> None:
         self.endian = endian
         self.longFmt = f"{self.endian}L"
         self.shortFmt = f"{self.endian}H"
diff --git a/src/PIL/WmfImagePlugin.py b/src/PIL/WmfImagePlugin.py
index fab3e26c587..25a4545db52 100644
--- a/src/PIL/WmfImagePlugin.py
+++ b/src/PIL/WmfImagePlugin.py
@@ -20,6 +20,8 @@
 # http://wvware.sourceforge.net/caolan/ora-wmf.html
 from __future__ import annotations
 
+from typing import IO
+
 from . import Image, ImageFile
 from ._binary import i16le as word
 from ._binary import si16le as short
@@ -161,7 +163,7 @@ def load(self, dpi=None):
         return super().load()
 
 
-def _save(im, fp, filename):
+def _save(im: Image.Image, fp: IO[bytes], filename: str) -> None:
     if _handler is None or not hasattr(_handler, "save"):
         msg = "WMF save handler not installed"
         raise OSError(msg)