diff --git a/.gitmodules b/.gitmodules
index 80ce81d..9f34e0d 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -16,3 +16,6 @@
 [submodule "book/external/TeachBooks"]
 	path = book/external/TeachBooks
 	url = https://github.com/TeachBooks/TeachBooks.git
+[submodule "book/external/Sphinx-Image-Inverter"]
+	path = book/external/Sphinx-Image-Inverter
+	url = https://github.com/TeachBooks/Sphinx-Image-Inverter.git
diff --git a/book/_toc.yml b/book/_toc.yml
index 1c03d88..671dca2 100644
--- a/book/_toc.yml
+++ b/book/_toc.yml
@@ -59,6 +59,7 @@ parts:
         sections:
         - file: features/widgets.ipynb
         - file: features/exercise_checking.ipynb
+      - file: external/Sphinx-Image-Inverter/README.md
 
   - caption: Examples
     chapters:
diff --git a/book/external/Nested-Books b/book/external/Nested-Books
index 4f72481..cc1d35d 160000
--- a/book/external/Nested-Books
+++ b/book/external/Nested-Books
@@ -1 +1 @@
-Subproject commit 4f72481f6a9b65c9b3bd22d0351b58b562f4802c
+Subproject commit cc1d35d73558dc5787ede7c4552fb35e9ba82a46
diff --git a/book/external/Sphinx-Image-Inverter b/book/external/Sphinx-Image-Inverter
new file mode 160000
index 0000000..61f101b
--- /dev/null
+++ b/book/external/Sphinx-Image-Inverter
@@ -0,0 +1 @@
+Subproject commit 61f101bd1fcf9bd8d2990e72b86e38499e0f3f04
diff --git a/book/external/TeachBooks b/book/external/TeachBooks
index c802630..f6968d6 160000
--- a/book/external/TeachBooks
+++ b/book/external/TeachBooks
@@ -1 +1 @@
-Subproject commit c802630d700f579eff2ac990496503bdda57ca3b
+Subproject commit f6968d6284d5f75950e502c50c6778d08d0fdf1f
diff --git a/book/external/Useful_python_code b/book/external/Useful_python_code
index c8327b3..8c7d765 160000
--- a/book/external/Useful_python_code
+++ b/book/external/Useful_python_code
@@ -1 +1 @@
-Subproject commit c8327b3e2cc68d44958974a47c940bc89f4bb32b
+Subproject commit 8c7d765f3a06b18517b315455ae7f5dc9230748c
diff --git a/book/external/deploy-book-workflow b/book/external/deploy-book-workflow
index 081491b..f4e88d5 160000
--- a/book/external/deploy-book-workflow
+++ b/book/external/deploy-book-workflow
@@ -1 +1 @@
-Subproject commit 081491b5f7bd0beecb5663228eaf5ab80b9dd57c
+Subproject commit f4e88d59f4e1809547e14fcdfc1ae5c512eec847
diff --git a/book/external/template b/book/external/template
index 775c868..080483e 160000
--- a/book/external/template
+++ b/book/external/template
@@ -1 +1 @@
-Subproject commit 775c8680d3d2e1b1720cffd13628bf2a57af6f8a
+Subproject commit 080483e6865edff26fd125382bac99b13e4d8539