diff --git a/torchvision/datasets/_optical_flow.py b/torchvision/datasets/_optical_flow.py
index bc26f51dc75..c7663258899 100644
--- a/torchvision/datasets/_optical_flow.py
+++ b/torchvision/datasets/_optical_flow.py
@@ -3,6 +3,7 @@
 from abc import ABC, abstractmethod
 from glob import glob
 from pathlib import Path
+from typing import Callable, List, Optional, Tuple, Union
 
 import numpy as np
 import torch
@@ -13,6 +14,10 @@
 from .vision import VisionDataset
 
 
+T1 = Tuple[Image.Image, Image.Image, Optional[np.ndarray], Optional[np.ndarray]]
+T2 = Tuple[Image.Image, Image.Image, Optional[np.ndarray]]
+
+
 __all__ = (
     "KittiFlow",
     "Sintel",
@@ -28,26 +33,26 @@ class FlowDataset(ABC, VisionDataset):
     # and it's up to whatever consumes the dataset to decide what valid_flow_mask should be.
     _has_builtin_flow_mask = False
 
-    def __init__(self, root, transforms=None):
+    def __init__(self, root: str, transforms: Optional[Callable] = None) -> None:
 
         super().__init__(root=root)
         self.transforms = transforms
 
-        self._flow_list = []
-        self._image_list = []
+        self._flow_list: List[str] = []
+        self._image_list: List[List[str]] = []
 
-    def _read_img(self, file_name):
+    def _read_img(self, file_name: str) -> Image.Image:
         img = Image.open(file_name)
         if img.mode != "RGB":
             img = img.convert("RGB")
         return img
 
     @abstractmethod
-    def _read_flow(self, file_name):
+    def _read_flow(self, file_name: str):
         # Return the flow or a tuple with the flow and the valid_flow_mask if _has_builtin_flow_mask is True
         pass
 
-    def __getitem__(self, index):
+    def __getitem__(self, index: int) -> Union[T1, T2]:
 
         img1 = self._read_img(self._image_list[index][0])
         img2 = self._read_img(self._image_list[index][1])
@@ -70,10 +75,10 @@ def __getitem__(self, index):
         else:
             return img1, img2, flow
 
-    def __len__(self):
+    def __len__(self) -> int:
         return len(self._image_list)
 
-    def __rmul__(self, v):
+    def __rmul__(self, v: int) -> torch.utils.data.ConcatDataset:
         return torch.utils.data.ConcatDataset([self] * v)
 
 
@@ -118,7 +123,13 @@ class Sintel(FlowDataset):
             return a built-in valid mask, such as :class:`~torchvision.datasets.KittiFlow`.
     """
 
-    def __init__(self, root, split="train", pass_name="clean", transforms=None):
+    def __init__(
+        self,
+        root: str,
+        split: str = "train",
+        pass_name: str = "clean",
+        transforms: Optional[Callable] = None,
+    ) -> None:
         super().__init__(root=root, transforms=transforms)
 
         verify_str_arg(split, "split", valid_values=("train", "test"))
@@ -139,7 +150,7 @@ def __init__(self, root, split="train", pass_name="clean", transforms=None):
                 if split == "train":
                     self._flow_list += sorted(glob(str(flow_root / scene / "*.flo")))
 
-    def __getitem__(self, index):
+    def __getitem__(self, index: int) -> Union[T1, T2]:
         """Return example at given index.
 
         Args:
@@ -154,7 +165,7 @@ def __getitem__(self, index):
         """
         return super().__getitem__(index)
 
-    def _read_flow(self, file_name):
+    def _read_flow(self, file_name: str) -> np.ndarray:
         return _read_flo(file_name)
 
 
@@ -180,7 +191,7 @@ class KittiFlow(FlowDataset):
 
     _has_builtin_flow_mask = True
 
-    def __init__(self, root, split="train", transforms=None):
+    def __init__(self, root: str, split: str = "train", transforms: Optional[Callable] = None) -> None:
         super().__init__(root=root, transforms=transforms)
 
         verify_str_arg(split, "split", valid_values=("train", "test"))
@@ -200,7 +211,7 @@ def __init__(self, root, split="train", transforms=None):
         if split == "train":
             self._flow_list = sorted(glob(str(root / "flow_occ" / "*_10.png")))
 
-    def __getitem__(self, index):
+    def __getitem__(self, index: int) -> Union[T1, T2]:
         """Return example at given index.
 
         Args:
@@ -215,7 +226,7 @@ def __getitem__(self, index):
         """
         return super().__getitem__(index)
 
-    def _read_flow(self, file_name):
+    def _read_flow(self, file_name: str) -> Tuple[np.ndarray, np.ndarray]:
         return _read_16bits_png_with_flow_and_valid_mask(file_name)
 
 
@@ -245,7 +256,7 @@ class FlyingChairs(FlowDataset):
             return a built-in valid mask, such as :class:`~torchvision.datasets.KittiFlow`.
     """
 
-    def __init__(self, root, split="train", transforms=None):
+    def __init__(self, root: str, split: str = "train", transforms: Optional[Callable] = None) -> None:
         super().__init__(root=root, transforms=transforms)
 
         verify_str_arg(split, "split", valid_values=("train", "val"))
@@ -268,7 +279,7 @@ def __init__(self, root, split="train", transforms=None):
                 self._flow_list += [flows[i]]
                 self._image_list += [[images[2 * i], images[2 * i + 1]]]
 
-    def __getitem__(self, index):
+    def __getitem__(self, index: int) -> Union[T1, T2]:
         """Return example at given index.
 
         Args:
@@ -283,7 +294,7 @@ def __getitem__(self, index):
         """
         return super().__getitem__(index)
 
-    def _read_flow(self, file_name):
+    def _read_flow(self, file_name: str) -> np.ndarray:
         return _read_flo(file_name)
 
 
@@ -316,7 +327,14 @@ class FlyingThings3D(FlowDataset):
             return a built-in valid mask, such as :class:`~torchvision.datasets.KittiFlow`.
     """
 
-    def __init__(self, root, split="train", pass_name="clean", camera="left", transforms=None):
+    def __init__(
+        self,
+        root: str,
+        split: str = "train",
+        pass_name: str = "clean",
+        camera: str = "left",
+        transforms: Optional[Callable] = None,
+    ) -> None:
         super().__init__(root=root, transforms=transforms)
 
         verify_str_arg(split, "split", valid_values=("train", "test"))
@@ -359,7 +377,7 @@ def __init__(self, root, split="train", pass_name="clean", camera="left", transf
                         self._image_list += [[images[i + 1], images[i]]]
                         self._flow_list += [flows[i + 1]]
 
-    def __getitem__(self, index):
+    def __getitem__(self, index: int) -> Union[T1, T2]:
         """Return example at given index.
 
         Args:
@@ -374,7 +392,7 @@ def __getitem__(self, index):
         """
         return super().__getitem__(index)
 
-    def _read_flow(self, file_name):
+    def _read_flow(self, file_name: str) -> np.ndarray:
         return _read_pfm(file_name)
 
 
@@ -401,7 +419,7 @@ class HD1K(FlowDataset):
 
     _has_builtin_flow_mask = True
 
-    def __init__(self, root, split="train", transforms=None):
+    def __init__(self, root: str, split: str = "train", transforms: Optional[Callable] = None) -> None:
         super().__init__(root=root, transforms=transforms)
 
         verify_str_arg(split, "split", valid_values=("train", "test"))
@@ -426,10 +444,10 @@ def __init__(self, root, split="train", transforms=None):
                 "Could not find the HD1K images. Please make sure the directory structure is correct."
             )
 
-    def _read_flow(self, file_name):
+    def _read_flow(self, file_name: str) -> Tuple[np.ndarray, np.ndarray]:
         return _read_16bits_png_with_flow_and_valid_mask(file_name)
 
-    def __getitem__(self, index):
+    def __getitem__(self, index: int) -> Union[T1, T2]:
         """Return example at given index.
 
         Args:
@@ -445,7 +463,7 @@ def __getitem__(self, index):
         return super().__getitem__(index)
 
 
-def _read_flo(file_name):
+def _read_flo(file_name: str) -> np.ndarray:
     """Read .flo file in Middlebury format"""
     # Code adapted from:
     # http://stackoverflow.com/questions/28013200/reading-middlebury-flow-files-with-python-bytes-array-numpy
@@ -462,7 +480,7 @@ def _read_flo(file_name):
         return data.reshape(h, w, 2).transpose(2, 0, 1)
 
 
-def _read_16bits_png_with_flow_and_valid_mask(file_name):
+def _read_16bits_png_with_flow_and_valid_mask(file_name: str) -> Tuple[np.ndarray, np.ndarray]:
 
     flow_and_valid = _read_png_16(file_name).to(torch.float32)
     flow, valid_flow_mask = flow_and_valid[:2, :, :], flow_and_valid[2, :, :]