project.json

## project.json
{
"frameworks": {
  "net46":{
    "dependencies": {
      "ImageResizer": "4.1.9"
    }
  }
 }
}

## run.csx
#r "Microsoft.WindowsAzure.Storage"
#r "Newtonsoft.Json"

using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using Microsoft.WindowsAzure.Storage;
using Microsoft.WindowsAzure.Storage.Blob;
using ImageResizer;
using ImageResizer.ExtensionMethods;

static string s_storageAccountConnectionString = System.Environment.GetEnvironmentVariable("blogBlobImageStorage");

public static async Task Run(JObject eventGridEvent, TraceWriter log)
{
    log.Info(eventGridEvent.ToString(Formatting.Indented));

    // Instructions to resize the blob image.
    var instructions = new Instructions
    {
        Width = 350,
        Height = 350,
        Mode = FitMode.Max
    };

    var url = eventGridEvent["data"]["url"].ToString();
    if(url.Contains("_thumb.jpg"))
        return;

    // Get the blobname from the event's JObject.
    var blobName = GetBlobNameFromUrl(url);

    // Retrieve storage account from connection string.
    var storageAccount = CloudStorageAccount.Parse(s_storageAccountConnectionString);

    // Create the blob client.
    var blobClient = storageAccount.CreateCloudBlobClient();

    // Retrieve reference to a previously created container.
    var container = blobClient.GetContainerReference("blog");

    // Create reference to a blob named "blobName".
    var blockBlob = container.GetBlockBlobReference(blobName);
    var inputStream = await blockBlob.OpenReadAsync();

    var blockBlobThumb = container.GetBlockBlobReference(blobName.Replace(".jpg","_thumb.jpg"));
    if(blockBlobThumb.Exists())
        return;

    using(MemoryStream myStream = new MemoryStream())
    {
        // Resize the image with the given instructions into the stream.
        ImageBuilder.Current.Build(new ImageJob(inputStream, myStream, instructions));

        // Reset the stream's position to the beginning.
        myStream.Position = 0;

        // Write the stream to the new blob.
        await blockBlobThumb.UploadFromStreamAsync(myStream);
    }

    blockBlobThumb.Properties.ContentType = "image/jpeg";
    blockBlobThumb.SetProperties();
}

private static string GetBlobNameFromUrl(string bloblUrl)
{
    var myUri = new Uri(bloblUrl);
    var myCloudBlob = new CloudBlob(myUri);
    return myCloudBlob.Name;
}