diff --git a/ClosedXML/Excel/Drawings/XLPicture.cs b/ClosedXML/Excel/Drawings/XLPicture.cs
index c933076..0d54b51 100644
--- a/ClosedXML/Excel/Drawings/XLPicture.cs
+++ b/ClosedXML/Excel/Drawings/XLPicture.cs
@@ -233,7 +233,7 @@
 
         private String GetExtension(ImagePartType type)
         {
-            return type.ToString();
+            return type.ToString().ToLower();
         }
 
         public ImagePartType GetImagePartType()
diff --git a/ClosedXML_Tests/ClosedXML_Tests.csproj b/ClosedXML_Tests/ClosedXML_Tests.csproj
index e53b52b..47cca6a 100644
--- a/ClosedXML_Tests/ClosedXML_Tests.csproj
+++ b/ClosedXML_Tests/ClosedXML_Tests.csproj
@@ -78,6 +78,7 @@
     <Compile Include="Excel\CalcEngine\LookupTests.cs" />
     <Compile Include="Excel\CalcEngine\StatisticalTests.cs" />
     <Compile Include="Excel\CalcEngine\TextTests.cs" />
+    <Compile Include="Excel\ImageHandling\PictureTests.cs" />
     <Compile Include="Excel\Misc\XmlEncoderTests.cs" />
     <Compile Include="Excel\Loading\LoadingTests.cs" />
     <Compile Include="Excel\PageSetup\HeaderFooterTests.cs" />
@@ -272,7 +273,9 @@
     <EmbeddedResource Include="Resource\Examples\ImageHandling\ImageAnchors.xlsx" />
     <EmbeddedResource Include="Resource\Examples\ImageHandling\ImageFormats.xlsx" />
   </ItemGroup>
-  <ItemGroup />
+  <ItemGroup>
+    <EmbeddedResource Include="Resource\Images\ImageHandling.png" />
+  </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
        Other similar extension points exist, see Microsoft.Common.targets.
diff --git a/ClosedXML_Tests/Excel/ImageHandling/PictureTests.cs b/ClosedXML_Tests/Excel/ImageHandling/PictureTests.cs
new file mode 100644
index 0000000..bd48796
--- /dev/null
+++ b/ClosedXML_Tests/Excel/ImageHandling/PictureTests.cs
@@ -0,0 +1,91 @@
+using System;
+using System.IO;
+using System.Reflection;
+using ClosedXML.Excel;
+using ClosedXML.Excel.Drawings;
+using NUnit.Framework;
+
+namespace ClosedXML_Tests
+{
+    [TestFixture]
+    public class PictureTests
+    {
+        [Test]
+        public void XLMarkerTests()
+        {
+            IXLWorksheet ws = new XLWorkbook().Worksheets.Add("Sheet1");
+            XLMarker firstMarker = new XLMarker
+            {
+                ColumnId = 1,
+                RowId = 1,
+                ColumnOffset = 100,
+                RowOffset = 0
+            };
+
+            firstMarker.ColumnId = 10;
+
+            Assert.AreEqual(10, firstMarker.ColumnId);
+            Assert.AreEqual(1, firstMarker.RowId);
+            Assert.AreEqual(100, firstMarker.ColumnOffset);
+            Assert.AreEqual(0, firstMarker.RowOffset);
+            Assert.AreEqual(9, firstMarker.GetZeroBasedColumn());
+            Assert.AreEqual(0, firstMarker.GetZeroBasedRow());
+
+            Assert.Throws(typeof(ArgumentOutOfRangeException), delegate { firstMarker.RowId = 0; });
+            Assert.Throws(typeof(ArgumentOutOfRangeException), delegate { firstMarker.ColumnId = 0; });
+            Assert.Throws(typeof(ArgumentOutOfRangeException),
+                            delegate { firstMarker.RowId = XLHelper.MaxRowNumber + 1; });
+            Assert.Throws(typeof(ArgumentOutOfRangeException),
+                            delegate { firstMarker.ColumnId = XLHelper.MaxColumnNumber + 1; });
+        }
+
+        [Test]
+        public void XLPictureTests()
+        {
+            IXLWorksheet ws = new XLWorkbook().Worksheets.Add("Sheet1");
+            XLMarker firstMarker = new XLMarker
+            {
+                ColumnId = 1,
+                RowId = 1,
+                ColumnOffset = 100,
+                RowOffset = 0
+            };
+
+            using (Stream fs = Assembly.GetExecutingAssembly().GetManifestResourceStream("ClosedXML_Tests.Resource.Images.ImageHandling.png"))
+            {
+                XLPicture pic = new XLPicture
+                {
+                    IsAbsolute = false,
+                    ImageStream = fs,
+                    Name = "Image1",
+                    Type = "png",
+                    OffsetX = 200,
+                    OffsetY = 155
+                };
+
+                fs.Position = 0;
+                System.Drawing.Bitmap bitmap = new System.Drawing.Bitmap(fs);
+
+                // Get these values manually as they vary from machine to machine
+                float horizontalRes = bitmap.HorizontalResolution;
+                float verticalRes = bitmap.VerticalResolution;
+
+                pic.AddMarker(firstMarker);
+
+                Assert.AreEqual(false, pic.IsAbsolute);
+                Assert.AreEqual("Image1", pic.Name);
+                Assert.AreEqual("png", pic.Type);
+                Assert.AreEqual(1, pic.GetMarkers().Count);
+                Assert.AreNotEqual(null, new XLPicture().GetMarkers());
+                Assert.AreEqual((long)(914400 * 252 / horizontalRes), pic.Width);
+                Assert.AreEqual((long)(914400 * 152 / verticalRes), pic.Height);
+                Assert.AreEqual(252, pic.RawWidth);
+                Assert.AreEqual(152, pic.RawHeight);
+                Assert.AreEqual((long)(914400 * 200 / horizontalRes), pic.OffsetX);
+                Assert.AreEqual((long)(914400 * 155 / verticalRes), pic.OffsetY);
+                Assert.AreEqual(200, pic.RawOffsetX);
+                Assert.AreEqual(155, pic.RawOffsetY);
+            }
+        }
+    }
+}
diff --git a/ClosedXML_Tests/Resource/Images/ImageHandling.png b/ClosedXML_Tests/Resource/Images/ImageHandling.png
new file mode 100644
index 0000000..cf23e54
--- /dev/null
+++ b/ClosedXML_Tests/Resource/Images/ImageHandling.png
Binary files differ