diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7e4aab1..261fa14 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,6 +1,6 @@
 cmake_minimum_required (VERSION 3.2)
 project(libravatarserv
-        VERSION 0.4.3
+        VERSION 0.5.0
         LANGUAGES CXX
 )
 
diff --git a/README.md b/README.md
index 0aaa876..2936d09 100644
--- a/README.md
+++ b/README.md
@@ -12,7 +12,7 @@ images tied to email or OpenID addresses.
 * MD5 hashes
 * SHA256 hashes
 * Variable image size (`s` or `size`)
-* Default actions (`d` or `default`): 404, URL, mp/mm
+* Default actions (`d` or `default`): 404, URL, mp/mm, identicon
 
 The default behaviour for unknown users is to return a 404 error. If a default
 image is put in the avatar directory, that is returned instead. The default
diff --git a/src/image.cpp b/src/image.cpp
index 7a9835a..2be47b3 100644
--- a/src/image.cpp
+++ b/src/image.cpp
@@ -15,6 +15,8 @@
  */
 
 #include <iostream>
+#include <sstream>
+#include <array>
 #include "libravatarserv.hpp"
 
 using std::cout;
@@ -69,3 +71,61 @@ void image::write(Image &image)
     cout.flush();   // We need to flush before we use /dev/stdout directly.
     image.image.write("/dev/stdout");
 }
+
+Image image::identicon(const string &digest)
+{
+    const string sha256 = hash::sha256(digest);
+    Magick::Image img(Magick::Geometry(4, 4), Magick::Color("white"));
+    // The 16 named colors specified in HTML 14.01 minus white, silver and gray.
+    const std::array<Magick::Color, 13> colors =
+    {
+        Magick::Color("black"),
+        Magick::Color("red"),
+        Magick::Color("maroon"),
+        Magick::Color("yellow"),
+        Magick::Color("olive"),
+        Magick::Color("lime"),
+        Magick::Color("green"),
+        Magick::Color("aqua"),
+        Magick::Color("teal"),
+        Magick::Color("blue"),
+        Magick::Color("navy"),
+        Magick::Color("fuchsia"),
+        Magick::Color("purple")
+    };
+
+    try
+    {
+        std::uint64_t random = 0xffff;
+        for (uint64_t chunk = 0; chunk < 4; ++chunk)
+        {
+            std::stringstream ss;
+            ss << std::hex << sha256.substr(chunk * 16, 16);
+            random = (random / 2) + (static_cast<std::uint64_t>(ss.get()) / 2);
+        }
+
+        Magick::Color dotcolor = colors[random % 13];
+        for (uint8_t row = 0; row < 4; ++row)
+        {
+            for (uint8_t column = 0; column < 4; ++column)
+            {
+                std::stringstream ss;
+                uint16_t px;
+                ss << std::hex << sha256.substr(row * 4 + column, 4);
+                ss >> px;
+                if (px > 0x8000)
+                {
+                    img.pixelColor(column, row, dotcolor);
+                }
+            }
+        }
+    }
+    catch (const std::exception &e)
+    {
+        cerr << "Error: " << e.what() << endl;
+        return { 5, img };
+    }
+
+    img.magick("png");
+    return { 0, img };
+}
diff --git a/src/libravatarserv.cpp b/src/libravatarserv.cpp
index 554ef15..3863e15 100644
--- a/src/libravatarserv.cpp
+++ b/src/libravatarserv.cpp
@@ -71,8 +71,8 @@ int main()
                  avatar.fallback.substr(0, 2) == "mm")
         {
             // MD5 hash of 'mp'
-            image =  image::get("1f2dfa567dcf95833eddf7aec167fec7",
-                                avatar.size);
+            image = image::get("1f2dfa567dcf95833eddf7aec167fec7",
+                               avatar.size);
             if (image.error == 0)
             {
                 image::write(image);
@@ -80,7 +80,21 @@ int main()
             else
             {
                 cout << "Status: 404 Not Found\n\n";
-                cerr << "Mystery person not found.\n";
+                cerr << "Error: Mystery person not found.\n";
+            }
+        }
+        else if (avatar.fallback.substr(0, 9) == "identicon")
+        {
+            image = image::identicon(avatar.digest);
+            if (image.error == 0)
+            {
+                image.image.scale(Magick::Geometry(avatar.size, avatar.size));
+                image::write(image);
+            }
+            else
+            {
+                cout << "Status: 404 Not Found\n\n";
+                cerr << "Error: Couldn't generate identicon.\n";
             }
         }
         else
diff --git a/src/libravatarserv.hpp b/src/libravatarserv.hpp
index abc5465..ced0036 100644
--- a/src/libravatarserv.hpp
+++ b/src/libravatarserv.hpp
@@ -75,6 +75,7 @@ namespace image // image.cpp
 
     const Image get(const string &digest, const uint16_t size);
     void write(Image &image);
+    Image identicon(const string &digest);
 }
 
 #endif  // LIBRAVATARSERV_HPP