diff --git a/src/include/OpenImageIO/imageio.h b/src/include/OpenImageIO/imageio.h
index 927e15119b..4cd773501f 100644
--- a/src/include/OpenImageIO/imageio.h
+++ b/src/include/OpenImageIO/imageio.h
@@ -1778,6 +1778,16 @@ class OIIO_API ImageInput {
     /// `ImageInput*`.
     typedef ImageInput* (*Creator)();
 
+    /// Memory tracking method.
+    /// Return the total heap memory allocated by `ImageInput`.
+    /// Overridable version of heapsize defined in memory.h.
+    virtual size_t heapsize() const;
+
+    /// Memory tracking method.
+    /// Return the total memory footprint of `ImageInput`.
+    /// Overridable version of footprint defined in memory.h.
+    virtual size_t footprint() const;
+
 protected:
     ImageSpec m_spec;  // format spec of the current open subimage/MIPlevel
                        // BEWARE using m_spec directly -- not thread-safe
@@ -1886,7 +1896,7 @@ class OIIO_API ImageInput {
 
     void append_error(string_view message) const; // add to error message
 
-    /// declare a friend heapsize definition
+    /// declare friend heapsize and footprint definitions
     template <typename T> friend size_t pvt::heapsize(const T&);
 };
 
@@ -2570,6 +2580,16 @@ class OIIO_API ImageOutput {
     /// `ImageOutput*`.
     typedef ImageOutput* (*Creator)();
 
+    /// Memory tracking method.
+    /// Return the total heap memory allocated by `ImageOutput`.
+    /// Overridable version of heapsize defined in memory.h.
+    virtual size_t heapsize() const;
+
+    /// Memory tracking method.
+    /// Return the total memory footprint of `ImageOutput`.
+    /// Overridable version of footprint defined in memory.h.
+    virtual size_t footprint() const;
+
 protected:
     /// @{
     /// @name Helper functions for ImageOutput implementations.
@@ -2793,7 +2813,7 @@ class OIIO_API ImageOutput {
 
     void append_error(string_view message) const; // add to m_errmessage
 
-    /// declare a friend heapsize definition
+    /// declare friend heapsize and footprint definitions
     template <typename T> friend size_t pvt::heapsize(const T&);
 };
 
@@ -2804,11 +2824,13 @@ class OIIO_API ImageOutput {
 // heapsize specialization for `ImageSpec`
 template <> OIIO_API size_t pvt::heapsize<ImageSpec>(const ImageSpec&);
 
-// heapsize specialization for `ImageInput`
+// heapsize and footprint specializations for `ImageInput`
 template <> OIIO_API size_t pvt::heapsize<ImageInput>(const ImageInput&);
+template <> OIIO_API size_t pvt::footprint<ImageInput>(const ImageInput&);
 
-// heapsize specialization for `ImageOutput`
+// heapsize and footprint specializations for `ImageOutput`
 template <> OIIO_API size_t pvt::heapsize<ImageOutput>(const ImageOutput&);
+template <> OIIO_API size_t pvt::footprint<ImageOutput>(const ImageOutput&);
 
 
 
diff --git a/src/libOpenImageIO/imageinput.cpp b/src/libOpenImageIO/imageinput.cpp
index baddc36e08..c4aa28cdf0 100644
--- a/src/libOpenImageIO/imageinput.cpp
+++ b/src/libOpenImageIO/imageinput.cpp
@@ -1341,13 +1341,47 @@ ImageInput::check_open(const ImageSpec& spec, ROI range, uint64_t /*flags*/)
 
 
 
+template<>
+inline size_t
+pvt::heapsize<ImageInput::Impl>(const ImageInput::Impl& impl)
+{
+    return impl.m_io_local ? sizeof(Filesystem::IOProxy) : 0;
+}
+
+
+
+size_t
+ImageInput::heapsize() const
+{
+    size_t size = pvt::heapsize(m_impl);
+    size += pvt::heapsize(m_spec);
+    return size;
+}
+
+
+
+size_t
+ImageInput::footprint() const
+{
+    return sizeof(ImageInput) + heapsize();
+}
+
+
+
 template<>
 size_t
 pvt::heapsize<ImageInput>(const ImageInput& input)
 {
-    //! TODO: change ImageInput API to add a virtual heapsize() function
-    //! to allow per image input override, and call that function here.
-    return pvt::heapsize(input.m_spec);
+    return input.heapsize();
+}
+
+
+
+template<>
+size_t
+pvt::footprint<ImageInput>(const ImageInput& input)
+{
+    return input.footprint();
 }
 
 
diff --git a/src/libOpenImageIO/imageoutput.cpp b/src/libOpenImageIO/imageoutput.cpp
index 002429fc93..f233b395b8 100644
--- a/src/libOpenImageIO/imageoutput.cpp
+++ b/src/libOpenImageIO/imageoutput.cpp
@@ -1021,13 +1021,47 @@ ImageOutput::check_open(OpenMode mode, const ImageSpec& userspec, ROI range,
 
 
 
+template<>
+inline size_t
+pvt::heapsize<ImageOutput::Impl>(const ImageOutput::Impl& impl)
+{
+    return impl.m_io_local ? sizeof(Filesystem::IOProxy) : 0;
+}
+
+
+
+size_t
+ImageOutput::heapsize() const
+{
+    size_t size = pvt::heapsize(m_impl);
+    size += pvt::heapsize(m_spec);
+    return size;
+}
+
+
+
+size_t
+ImageOutput::footprint() const
+{
+    return sizeof(ImageOutput) + heapsize();
+}
+
+
+
 template<>
 size_t
 pvt::heapsize<ImageOutput>(const ImageOutput& output)
 {
-    //! TODO: change ImageOutput API to add a virtual heapsize() function
-    //! to allow per image output override, and call that function here.
-    return pvt::heapsize(output.m_spec);
+    return output.heapsize();
+}
+
+
+
+template<>
+size_t
+pvt::footprint<ImageOutput>(const ImageOutput& output)
+{
+    return output.footprint();
 }