diff --git a/.gitmodules b/.gitmodules
index 2efd269e..6b4c46db 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -3,3 +3,23 @@
 	url = https://github.com/Orc/discount.git
 	branch = master
 	ignore = untracked
+[submodule "tools/pngquant"]
+	path = tools/pngquant
+	url = https://github.com/pornel/pngquant.git
+	branch = master
+	ignore = untracked
+[submodule "tools/zopfli"]
+	path = tools/zopfli
+	url = https://github.com/google/zopfli.git
+	branch = master
+	ignore = untracked
+[submodule "tools/libpng"]
+	path = tools/libpng
+	url = https://github.com/glennrp/libpng.git
+	branch = libpng16
+	ignore = untracked
+[submodule "tools/zlib"]
+	path = tools/zlib
+	url = https://github.com/madler/zlib.git
+	branch = master
+	ignore = untracked
diff --git a/tools/libpng b/tools/libpng
new file mode 160000
index 00000000..ed5a01d9
--- /dev/null
+++ b/tools/libpng
@@ -0,0 +1 @@
+Subproject commit ed5a01d922269f1241afeb5d19fde4330d481964
diff --git a/tools/pngquant b/tools/pngquant
new file mode 160000
index 00000000..6ad92e43
--- /dev/null
+++ b/tools/pngquant
@@ -0,0 +1 @@
+Subproject commit 6ad92e439f5ba3e49da0c06773c752bb89068fd1
diff --git a/tools/zlib b/tools/zlib
new file mode 160000
index 00000000..50893291
--- /dev/null
+++ b/tools/zlib
@@ -0,0 +1 @@
+Subproject commit 50893291621658f355bc5b4d450a8d06a563053d
diff --git a/tools/zopfli b/tools/zopfli
new file mode 160000
index 00000000..6818a085
--- /dev/null
+++ b/tools/zopfli
@@ -0,0 +1 @@
+Subproject commit 6818a0859063b946094fb6f94732836404a0d89a