diff --git a/ImageResizer.Plugins.PngOptimizer/ImageResizer.Plugins.PngOptimizer.nuspec b/ImageResizer.Plugins.PngOptimizer/ImageResizer.Plugins.PngOptimizer.nuspec
index 57899ad..f1ec5be 100644
--- a/ImageResizer.Plugins.PngOptimizer/ImageResizer.Plugins.PngOptimizer.nuspec
+++ b/ImageResizer.Plugins.PngOptimizer/ImageResizer.Plugins.PngOptimizer.nuspec
@@ -2,13 +2,15 @@
 <package xmlns="http://schemas.microsoft.com/packaging/2012/06/nuspec.xsd">
     <metadata>
         <id>ImageResizer.Plugins.PngOptimizer</id>
-        <version>2.0.0</version>
+        <version>2.1.0</version>
         <title>ImageResizer.Plugins.PngOptimizer</title>
         <authors>Geta</authors>
         <owners>Geta</owners>
-        <requireLicenseAcceptance>false</requireLicenseAcceptance>
+        <requireLicenseAcceptance>true</requireLicenseAcceptance>
         <description>Implementation of nQuant for png optimization. http://nquant.codeplex.com</description>
         <copyright>Copyright © Geta 2015</copyright>
+        <licenseUrl>https://github.com/svenrog/ImageResizer.Plugins.PngOptimizer/blob/master/LICENCE</licenseUrl>
+        <projectUrl>https://github.com/svenrog/ImageResizer.Plugins.PngOptimizer</projectUrl>
         <dependencies>
             <group targetFramework=".NETFramework4.5">
                 <dependency id="ImageResizer" version="4.0.5" />
@@ -17,6 +19,6 @@
     </metadata>
     <files>
         <file src="content\web.config.transform" target="content\web.config.transform" />
-        <file src="bin\Release\ImageResizer.Plugins.PngOptimizer.dll" target="lib\net45\ImageResizer.Plugins.PngOptimizer.dll" />
+        <file src="bin\Release\ImageResizer.Plugins.PngOptimizer.dll" target="lib\net452\ImageResizer.Plugins.PngOptimizer.dll" />
     </files>
 </package>
\ No newline at end of file
diff --git a/ImageResizer.Plugins.PngOptimizer/LICENCE b/ImageResizer.Plugins.PngOptimizer/LICENCE.txt
similarity index 100%
rename from ImageResizer.Plugins.PngOptimizer/LICENCE
rename to ImageResizer.Plugins.PngOptimizer/LICENCE.txt
diff --git a/ImageResizer.Plugins.PngOptimizer/PngOptimizerPlugin.cs b/ImageResizer.Plugins.PngOptimizer/PngOptimizerPlugin.cs
index 141f0df..290a73f 100644
--- a/ImageResizer.Plugins.PngOptimizer/PngOptimizerPlugin.cs
+++ b/ImageResizer.Plugins.PngOptimizer/PngOptimizerPlugin.cs
@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Drawing;
 using System.Drawing.Imaging;
+using System.IO;
 using ImageResizer.Configuration;
 using ImageResizer.Plugins.PngOptimizer.Analyzers;
 using ImageResizer.Plugins.PngOptimizer.Quantization;
@@ -103,27 +104,44 @@ protected virtual byte GetDitherSetting(ImageState state)
 
         protected virtual bool DetermineEnabled(ImageState state)
         {
-            if (state.destBitmap == null) return false;
+            if (state == null) return false;
             if (state.settings == null) return false;
+            if (state.destBitmap == null) return false;
 
-            var setting = state.settings["optimizePng"];
+            var setting = state.settings["optimizePng"] ?? string.Empty;
 
-            if (string.IsNullOrEmpty(setting)) return IsPngFile(state);
             if (setting == "0") return false;
             if (setting.Equals("false", StringComparison.InvariantCultureIgnoreCase)) return false;
 
-            return true;
+            return IsPngFile(state);
         }
 
         protected virtual bool IsPngFile(ImageState state)
         {
-            if (state.Job == null) return false;
-
-            var extension = state.Job.ResultFileExtension ?? string.Empty;
+            var extension = state.Job?.ResultFileExtension ??
+                            GetExtension(state.sourceBitmap) ??
+                            string.Empty;
 
             return extension.Equals("png", StringComparison.InvariantCultureIgnoreCase);
         }
 
+        public string GetExtension(Bitmap source)
+        {
+            if (source == null)
+                return null;
+
+            var tag = source.Tag as BitmapTag;
+            if (tag == null)
+                return null;
+
+            var path = tag.Path;
+            if (string.IsNullOrEmpty(path))
+                return null;
+
+            return Path.GetExtension(path)
+                       .TrimStart('.');
+        }
+
         protected virtual bool DetermineDebug(ImageState state)
         {
             var setting = state.settings["optimizePngDebug"];
diff --git a/ImageResizer.Plugins.PngOptimizer/Properties/AssemblyInfo.cs b/ImageResizer.Plugins.PngOptimizer/Properties/AssemblyInfo.cs
index 7a27898..8f32a39 100644
--- a/ImageResizer.Plugins.PngOptimizer/Properties/AssemblyInfo.cs
+++ b/ImageResizer.Plugins.PngOptimizer/Properties/AssemblyInfo.cs
@@ -31,5 +31,5 @@
 // You can specify all the values or you can default the Build and Revision Numbers 
 // by using the '*' as shown below:
 // [assembly: AssemblyVersion("1.0.*")]
-[assembly: AssemblyVersion("2.0.0.0")]
-[assembly: AssemblyFileVersion("2.0.0.0")]
+[assembly: AssemblyVersion("2.1.0.0")]
+[assembly: AssemblyFileVersion("2.1.0.0")]
diff --git a/build-packages.ps1 b/build-packages.ps1
new file mode 100644
index 0000000..67c81ef
--- /dev/null
+++ b/build-packages.ps1
@@ -0,0 +1,5 @@
+cd .\.nuget
+
+.\nuget.exe pack ..\ImageResizer.Plugins.PngOptimizer\ImageResizer.Plugins.PngOptimizer.csproj -Properties Configuration=Release
+
+cd ..\
\ No newline at end of file
diff --git a/packages.config b/packages.config
new file mode 100644
index 0000000..0901fde
--- /dev/null
+++ b/packages.config
@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<packages>
+  <package id="NuGet.CommandLine" version="2.8.2" />
+</packages>
\ No newline at end of file