diff --git a/src/ImageProcessor.Web/Helpers/ProcessQueryStringEventArgs.cs b/src/ImageProcessor.Web/Helpers/ProcessQueryStringEventArgs.cs
new file mode 100644
index 000000000..3bdda5c72
--- /dev/null
+++ b/src/ImageProcessor.Web/Helpers/ProcessQueryStringEventArgs.cs
@@ -0,0 +1,25 @@
+// --------------------------------------------------------------------------------------------------------------------
+// <copyright file="ProcessQueryStringEventArgs.cs" company="James South">
+//   Copyright (c) James South.
+//   Licensed under the Apache License, Version 2.0.
+// </copyright>
+// <summary>
+//   The process querystring event arguments.
+// </summary>
+// --------------------------------------------------------------------------------------------------------------------
+
+namespace ImageProcessor.Web.Helpers
+{
+    using System;
+
+    /// <summary>
+    /// The process querystring event arguments.
+    /// </summary>
+    public class ProcessQueryStringEventArgs : EventArgs
+    {
+        /// <summary>
+        /// Gets or sets the querystring.
+        /// </summary>
+        public string Querystring { get; set; }
+    }
+}
diff --git a/src/ImageProcessor.Web/HttpModules/ImageProcessingModule.cs b/src/ImageProcessor.Web/HttpModules/ImageProcessingModule.cs
index de1a64382..2b06b2b7c 100644
--- a/src/ImageProcessor.Web/HttpModules/ImageProcessingModule.cs
+++ b/src/ImageProcessor.Web/HttpModules/ImageProcessingModule.cs
@@ -107,11 +107,28 @@ namespace ImageProcessor.Web.HttpModules
         }
         #endregion
 
+        /// <summary>
+        /// The process querystring event handler.
+        /// </summary>
+        /// <param name="sender">
+        /// The sender.
+        /// </param>
+        /// <param name="e">
+        /// The <see cref="ProcessQueryStringEventArgs"/>.
+        /// </param>
+        /// <returns>Returns the processed querystring.</returns>
+        public delegate string ProcessQuerystringEventHandler(object sender, ProcessQueryStringEventArgs e);
+
         /// <summary>
         /// The event that is called when a new image is processed.
         /// </summary>
         public static event EventHandler<PostProcessingEventArgs> OnPostProcessing;
 
+        /// <summary>
+        /// The event that is called when a querystring is processed.
+        /// </summary>
+        public static event ProcessQuerystringEventHandler OnProcessQuerystring;
+
         #region IHttpModule Members
         /// <summary>
         /// Initializes a module and prepares it to handle requests.
@@ -327,6 +344,9 @@ namespace ImageProcessor.Web.HttpModules
                     }
                 }
 
+                // Replace any presets in the querystring with the actual value.
+                queryString = this.ReplacePresetsInQueryString(queryString);
+
                 // If the current service doesn't require a prefix, don't fetch it.
                 // Let the static file handler take over.
                 if (string.IsNullOrWhiteSpace(currentService.Prefix) && string.IsNullOrWhiteSpace(queryString))
@@ -334,9 +354,6 @@ namespace ImageProcessor.Web.HttpModules
                     return;
                 }
 
-                // Replace any presets in the querystring with the actual value.
-                queryString = this.ReplacePresetsInQueryString(queryString);
-
                 string parts = !string.IsNullOrWhiteSpace(urlParameters) ? "?" + urlParameters : string.Empty;
                 string fullPath = string.Format("{0}{1}?{2}", requestPath, parts, queryString);
                 object resourcePath;
@@ -526,18 +543,29 @@ namespace ImageProcessor.Web.HttpModules
         /// </returns>
         private string ReplacePresetsInQueryString(string queryString)
         {
-            foreach (Match match in PresetRegex.Matches(queryString))
+            if (!string.IsNullOrWhiteSpace(queryString))
             {
-                if (match.Success)
+                foreach (Match match in PresetRegex.Matches(queryString))
                 {
-                    string preset = match.Value.Split('=')[1];
+                    if (match.Success)
+                    {
+                        string preset = match.Value.Split('=')[1];
 
-                    // We use the processor config system to store the preset values.
-                    string replacements = ImageProcessorConfiguration.Instance.GetPresetSettings(preset);
-                    queryString = Regex.Replace(queryString, preset, replacements ?? string.Empty);
+                        // We use the processor config system to store the preset values.
+                        string replacements = ImageProcessorConfiguration.Instance.GetPresetSettings(preset);
+                        queryString = Regex.Replace(queryString, preset, replacements ?? string.Empty);
+                    }
                 }
             }
 
+            // Fire the process querystring event.
+            ProcessQuerystringEventHandler handler = OnProcessQuerystring;
+            if (handler != null)
+            {
+                ProcessQueryStringEventArgs args = new ProcessQueryStringEventArgs { Querystring = queryString ?? string.Empty };
+                queryString = handler(this, args);
+            }
+
             return queryString;
         }
 
diff --git a/src/ImageProcessor.Web/ImageProcessor.Web.csproj b/src/ImageProcessor.Web/ImageProcessor.Web.csproj
index 1c7e29c40..9ad80addb 100644
--- a/src/ImageProcessor.Web/ImageProcessor.Web.csproj
+++ b/src/ImageProcessor.Web/ImageProcessor.Web.csproj
@@ -46,6 +46,7 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="Caching\CachedImage.cs" />
+    <Compile Include="Helpers\ProcessQueryStringEventArgs.cs" />
     <Compile Include="Processors\DetectEdges.cs" />
     <Compile Include="Processors\EntropyCrop.cs" />
     <Compile Include="Processors\Hue.cs" />
diff --git a/src/TestWebsites/MVC/Global.asax.cs b/src/TestWebsites/MVC/Global.asax.cs
index 54afb402f..f72024ad9 100644
--- a/src/TestWebsites/MVC/Global.asax.cs
+++ b/src/TestWebsites/MVC/Global.asax.cs
@@ -10,6 +10,7 @@ namespace Test_Website_NET45
 {
     using System.Diagnostics;
     using System.Threading.Tasks;
+    using System.Web.UI.WebControls;
 
     using ImageProcessor.Web.Helpers;
     using ImageProcessor.Web.HttpModules;
@@ -28,7 +29,16 @@ namespace Test_Website_NET45
 
             // Test the post processing event.
             ImageProcessingModule.OnPostProcessing += (sender, args) => Debug.WriteLine(args.CachedImagePath);
-            //ImageProcessingModule.OnPostProcessing += this.WritePath;
+
+            ImageProcessingModule.OnProcessQuerystring += (sender, args) =>
+                {
+                    if (!args.Querystring.Contains("watermark"))
+                    {
+                        return args.Querystring += "watermark=protected&color=fff&fontsize=36&fontopacity=70textshadow=true&fontfamily=arial";
+                    }
+
+                    return args.Querystring;
+                };
         }
 
         private async void WritePath(object sender, PostProcessingEventArgs e)