diff --git a/samples/misc/NodeServicesExamples/Controllers/ResizeImage.cs b/samples/misc/NodeServicesExamples/Controllers/ResizeImage.cs
index c6b08b2..e0f498e 100644
--- a/samples/misc/NodeServicesExamples/Controllers/ResizeImage.cs
+++ b/samples/misc/NodeServicesExamples/Controllers/ResizeImage.cs
@@ -11,6 +11,7 @@ namespace NodeServicesExamples.Controllers
     public class ResizeImageController : Controller
     {
         private const int MaxDimension = 1000;
+        private static string[] AllowedMimeTypes = new[] { "image/jpeg", "image/png", "image/gif" };
 
         private IHostingEnvironment _environment;
         private INodeServices _nodeServices;
@@ -25,11 +26,18 @@ namespace NodeServicesExamples.Controllers
         public async Task<IActionResult> Index(string imagePath, int maxWidth, int maxHeight)
         {
             // Validate incoming params
-            if (maxWidth > MaxDimension || maxHeight > MaxDimension || (maxHeight <= 0 && maxWidth <= 0))
+            if (maxWidth < 0 || maxHeight < 0 || maxWidth > MaxDimension || maxHeight > MaxDimension
+                || (maxWidth + maxHeight) == 0)
             {
                 return BadRequest("Invalid dimensions");
             }
 
+            var mimeType = GetContentType(imagePath);
+            if (Array.IndexOf(AllowedMimeTypes, mimeType) < 0)
+            {
+                return BadRequest("Disallowed image format");
+            }
+
             // Locate source image on disk
             var fileInfo = _environment.WebRootFileProvider.GetFileInfo(imagePath);
             if (!fileInfo.Exists)
@@ -38,25 +46,19 @@ namespace NodeServicesExamples.Controllers
             }
 
             // Invoke Node and pipe the result to the response
-            var mimeType = GetContentType(imagePath);
-            var imageStream = await _nodeServices.Invoke<Stream>("./Node/resizeImage", fileInfo.PhysicalPath, mimeType, maxWidth, maxHeight);
+            var imageStream = await _nodeServices.Invoke<Stream>(
+                "./Node/resizeImage",
+                fileInfo.PhysicalPath,
+                mimeType,
+                maxWidth,
+                maxHeight);
             return File(imageStream, mimeType);
         }
 
         private string GetContentType(string path)
         {
             string result;
-            if (!new FileExtensionContentTypeProvider().TryGetContentType(path, out result))
-            {
-                result = "application/octet-stream";
-            }
-
-            return result;
-        }
-
-        private class ResizeImageResult
-        {
-            public string Base64 { get; set; }
+            return new FileExtensionContentTypeProvider().TryGetContentType(path, out result) ? result : null;
         }
     }
 }
diff --git a/samples/misc/NodeServicesExamples/Node/resizeImage.js b/samples/misc/NodeServicesExamples/Node/resizeImage.js
index 77fdb1b..207b149 100644
--- a/samples/misc/NodeServicesExamples/Node/resizeImage.js
+++ b/samples/misc/NodeServicesExamples/Node/resizeImage.js
@@ -1,7 +1,8 @@
 var sharp = require('sharp');
 
 module.exports = function(result, physicalPath, mimeType, maxWidth, maxHeight) {
+    // Invoke the 'sharp' NPM module, and have it pipe the resulting image data back to .NET
     sharp(physicalPath)
-        .resize(maxWidth > 0 ? maxWidth : null, maxHeight > 0 ? maxHeight : null)
+        .resize(maxWidth || null, maxHeight || null)
         .pipe(result.stream);
 }