diff --git a/src/PIL/EpsImagePlugin.py b/src/PIL/EpsImagePlugin.py
index b96ce9603a3..195dde86367 100644
--- a/src/PIL/EpsImagePlugin.py
+++ b/src/PIL/EpsImagePlugin.py
@@ -360,7 +360,7 @@ def check_required_header_comments():
 
         check_required_header_comments()
 
-        if not self._size:
+        if not self.size:
             msg = "cannot determine EPS bounding box"
             raise OSError(msg)
 
diff --git a/src/PIL/GifImagePlugin.py b/src/PIL/GifImagePlugin.py
index 92074b0d49e..d2e33271d18 100644
--- a/src/PIL/GifImagePlugin.py
+++ b/src/PIL/GifImagePlugin.py
@@ -262,7 +262,7 @@ def _seek(self, frame, update_image=True):
                 x1, y1 = x0 + i16(s, 4), y0 + i16(s, 6)
                 if (x1 > self.size[0] or y1 > self.size[1]) and update_image:
                     self._size = max(x1, self.size[0]), max(y1, self.size[1])
-                    Image._decompression_bomb_check(self._size)
+                    Image._decompression_bomb_check(self.size)
                 frame_dispose_extent = x0, y0, x1, y1
                 flags = s[8]
 
@@ -328,8 +328,8 @@ def _seek(self, frame, update_image=True):
                         self._mode = "RGBA"
                         del self.info["transparency"]
                     else:
-                        self._mode = "RGB"
                         self.im = self.im.convert("RGB", Image.Dither.FLOYDSTEINBERG)
+                        self._mode = "RGB"
 
         def _rgb(color):
             if self._frame_palette:
diff --git a/src/PIL/IcnsImagePlugin.py b/src/PIL/IcnsImagePlugin.py
index 0aa4f7a8458..5df3449b1c2 100644
--- a/src/PIL/IcnsImagePlugin.py
+++ b/src/PIL/IcnsImagePlugin.py
@@ -261,11 +261,7 @@ def _open(self):
             self.best_size[1] * self.best_size[2],
         )
 
-    @property
-    def size(self):
-        return self._size
-
-    @size.setter
+    @Image.Image.size.setter
     def size(self, value):
         info_size = value
         if info_size not in self.info["sizes"] and len(info_size) == 2:
@@ -283,7 +279,10 @@ def size(self, value):
         if info_size not in self.info["sizes"]:
             msg = "This is not one of the allowed sizes of this image"
             raise ValueError(msg)
-        self._size = value
+        if value != self.size:
+            self.im = None
+            self.pyaccess = None
+            self._size = value
 
     def load(self):
         if len(self.size) == 3:
@@ -306,7 +305,7 @@ def load(self):
 
         self.im = im.im
         self._mode = im.mode
-        self.size = im.size
+        self._size = im.size
 
         return px
 
diff --git a/src/PIL/IcoImagePlugin.py b/src/PIL/IcoImagePlugin.py
index 0445a2ab22f..3d75afb627a 100644
--- a/src/PIL/IcoImagePlugin.py
+++ b/src/PIL/IcoImagePlugin.py
@@ -310,36 +310,36 @@ def _open(self):
         self.size = self.ico.entry[0]["dim"]
         self.load()
 
-    @property
-    def size(self):
-        return self._size
-
-    @size.setter
+    @Image.Image.size.setter
     def size(self, value):
         if value not in self.info["sizes"]:
             msg = "This is not one of the allowed sizes of this image"
             raise ValueError(msg)
-        self._size = value
+        if value != self.size:
+            self.im = None
+            self.pyaccess = None
+            self._size = value
 
     def load(self):
         if self.im is not None and self.im.size == self.size:
             # Already loaded
             return Image.Image.load(self)
-        im = self.ico.getimage(self.size)
+        size_to_load = self.size
+        im = self.ico.getimage(size_to_load)
         # if tile is PNG, it won't really be loaded yet
         im.load()
         self.im = im.im
         self.pyaccess = None
         self._mode = im.mode
-        if im.size != self.size:
+        if im.size != size_to_load:
             warnings.warn("Image was not the expected size")
 
-            index = self.ico.getentryindex(self.size)
+            index = self.ico.getentryindex(size_to_load)
             sizes = list(self.info["sizes"])
             sizes[index] = im.size
             self.info["sizes"] = set(sizes)
 
-            self.size = im.size
+            self._size = im.size
 
     def load_seek(self):
         # Flag the ImageFile.Parser so that it
diff --git a/src/PIL/Image.py b/src/PIL/Image.py
index 476ed012278..f09429875df 100644
--- a/src/PIL/Image.py
+++ b/src/PIL/Image.py
@@ -480,16 +480,24 @@ class Image:
 
     def __init__(self):
         # FIXME: take "new" parameters / other image?
-        # FIXME: turn mode and size into delegating properties?
         self.im = None
-        self._mode = ""
-        self._size = (0, 0)
+        # do not directly change __mode; use _mode instead
+        self.__mode = ""
+        # do not directly change __size; use _size instead
+        self.__size = (0, 0)
         self.palette = None
         self.info = {}
         self.readonly = 0
         self.pyaccess = None
         self._exif = None
 
+    def _use_im_values(self):
+        """
+        Whether or not to try using values from self.im
+        in addition to the values in this class.
+        """
+        return self.im is not None
+
     @property
     def width(self):
         return self.size[0]
@@ -500,11 +508,31 @@ def height(self):
 
     @property
     def size(self):
-        return self._size
+        if self._use_im_values():
+            return self.im.size
+        return self.__size
+
+    def _size(self, value):
+        # set im.size first in case it raises an exception
+        if self._use_im_values():
+            self.im.size = value
+        self.__size = value
+
+    _size = property(fset=_size)
 
     @property
     def mode(self):
-        return self._mode
+        if self._use_im_values():
+            return self.im.mode
+        return self.__mode
+
+    def _mode(self, value):
+        # set im.mode first in case it raises an exception
+        if self._use_im_values():
+            self.im.mode = value
+        self.__mode = value
+
+    _mode = property(fset=_mode)
 
     def _new(self, im):
         new = Image()
diff --git a/src/PIL/ImageFile.py b/src/PIL/ImageFile.py
index 8e4f7dfb2c8..39187624971 100644
--- a/src/PIL/ImageFile.py
+++ b/src/PIL/ImageFile.py
@@ -139,6 +139,9 @@ def get_format_mimetype(self):
         if self.format is not None:
             return Image.MIME.get(self.format.upper())
 
+    def _use_im_values(self):
+        return self.tile is None and self.im is not None
+
     def __setstate__(self, state):
         self.tile = []
         super().__setstate__(state)
diff --git a/src/PIL/ImageOps.py b/src/PIL/ImageOps.py
index 17702778c13..92561860282 100644
--- a/src/PIL/ImageOps.py
+++ b/src/PIL/ImageOps.py
@@ -604,7 +604,7 @@ def exif_transpose(image, *, in_place=False):
         if in_place:
             image.im = transposed_image.im
             image.pyaccess = None
-            image._size = transposed_image._size
+            image._size = transposed_image.size
         exif_image = image if in_place else transposed_image
 
         exif = exif_image.getexif()
diff --git a/src/PIL/PcxImagePlugin.py b/src/PIL/PcxImagePlugin.py
index 854d9e83ee7..f4a636098a4 100644
--- a/src/PIL/PcxImagePlugin.py
+++ b/src/PIL/PcxImagePlugin.py
@@ -114,7 +114,7 @@ def _open(self):
         # Don't trust the passed in stride.
         # Calculate the approximate position for ourselves.
         # CVE-2020-35653
-        stride = (self._size[0] * bits + 7) // 8
+        stride = (self.size[0] * bits + 7) // 8
 
         # While the specification states that this must be even,
         # not all images follow this
diff --git a/src/PIL/QoiImagePlugin.py b/src/PIL/QoiImagePlugin.py
index 5c34075038f..e51e739af2e 100644
--- a/src/PIL/QoiImagePlugin.py
+++ b/src/PIL/QoiImagePlugin.py
@@ -32,7 +32,7 @@ def _open(self):
         self._mode = "RGB" if channels == 3 else "RGBA"
 
         self.fp.seek(1, os.SEEK_CUR)  # colorspace
-        self.tile = [("qoi", (0, 0) + self._size, self.fp.tell(), None)]
+        self.tile = [("qoi", (0, 0) + self.size, self.fp.tell(), None)]
 
 
 class QoiDecoder(ImageFile.PyDecoder):
diff --git a/src/_imaging.c b/src/_imaging.c
index e15cb89fcea..5c911d81a2e 100644
--- a/src/_imaging.c
+++ b/src/_imaging.c
@@ -3646,11 +3646,49 @@ _getattr_mode(ImagingObject *self, void *closure) {
     return PyUnicode_FromString(self->image->mode);
 }
 
+static int
+_setattr_mode(ImagingObject *self, PyObject *value, void *closure) {
+    if (value == NULL) {
+        self->image->mode[0] = '\0';
+        return 0;
+    }
+
+    const char *mode = PyUnicode_AsUTF8(value);
+    if (mode == NULL) {
+        return -1;
+    }
+    if (strlen(mode) >= IMAGING_MODE_LENGTH) {
+        PyErr_SetString(PyExc_ValueError, "given mode name is too long");
+        return -1;
+    }
+
+    strcpy(self->image->mode, mode);
+    return 0;
+}
+
 static PyObject *
 _getattr_size(ImagingObject *self, void *closure) {
     return Py_BuildValue("ii", self->image->xsize, self->image->ysize);
 }
 
+static int
+_setattr_size(ImagingObject *self, PyObject *value, void *closure) {
+    if (value == NULL) {
+        self->image->xsize = 0;
+        self->image->ysize = 0;
+        return 0;
+    }
+
+    int xsize, ysize;
+    if (!PyArg_ParseTuple(value, "ii", &xsize, &ysize)) {
+        return -1;
+    }
+
+    self->image->xsize = xsize;
+    self->image->ysize = ysize;
+    return 0;
+}
+
 static PyObject *
 _getattr_bands(ImagingObject *self, void *closure) {
     return PyLong_FromLong(self->image->bands);
@@ -3679,13 +3717,14 @@ _getattr_unsafe_ptrs(ImagingObject *self, void *closure) {
 };
 
 static struct PyGetSetDef getsetters[] = {
-    {"mode", (getter)_getattr_mode},
-    {"size", (getter)_getattr_size},
+    {"mode", (getter)_getattr_mode, (setter)_setattr_mode},
+    {"size", (getter)_getattr_size, (setter)_setattr_size},
     {"bands", (getter)_getattr_bands},
     {"id", (getter)_getattr_id},
     {"ptr", (getter)_getattr_ptr},
     {"unsafe_ptrs", (getter)_getattr_unsafe_ptrs},
-    {NULL}};
+    {NULL}
+};
 
 /* basic sequence semantics */