☁️ Powerful Cloud-Based Image Uploading with Watermark in .NET Core

Handling image uploads in web applications can get tricky — especially when you want to:

Optimize images for size and performance
Add a dynamic text watermark
Upload to a cloud provider like Cloudinary
Handle bulk uploads and deletions
Ensure clean logging and error handling

In this post, I’ll walk you through a robust service I built using Cloudinary + .NET Core that solves all of that — with extensibility and performance in mind.

✅ Features of This Service

This service is designed to handle all major image workflows for a backend API:

✅ Upload a single image with optional watermark
✅ Upload multiple images in parallel
✅ Resize & optimize images before uploading
✅ Add custom watermark text (like branding)
✅ Delete images from Cloudinary
✅ Full logging and error reporting
✅ Adjustable watermark style and quality

⚙️ Key Technologies Used

Cloudinary .NET SDK
System.Drawing for image resizing and optimization
ASP.NET Core + Dependency Injection
ILogger for clean logs
IFormFile for file handling in ASP.NET Core APIs

🧠 How It Works

🔹 1. Upload with Optimization

Before uploading, the image is:

Read from the stream
Resized based on predefined rules
Saved as optimized JPEG with 90% quality
Sent to Cloudinary using ImageUploadParams

var optimizedStream = await ConvertAndOptimizeImage(file);

🔹 2. Add Watermark

You can define a custom watermark using Cloudinary's transformation API:

new Transformation()
  .Overlay(new TextLayer("GOORFA.COM")
  .FontFamily("Arial")
  .FontSize(80)
  .FontWeight("bold"))
  .Gravity("center")
  .Opacity(60)
  .Color("#FFFFFF")
  .Flags("layer_apply");

🔹 3. Upload Multiple Images in Parallel

Uses Task.WhenAll() to efficiently upload many files at once:

var uploadTasks = files.Select(file => UploadImageAsync(file, folder));
await Task.WhenAll(uploadTasks);

🔹 4. Delete by Public ID

Clean removal of uploaded files using Cloudinary's destroy API:

var result = await _cloudinary.DestroyAsync(new DeletionParams(publicId));

📦 Sample Use Case

You can easily use this service in a controller like this:

[HttpPost("upload")]
public async Task<IActionResult> UploadImage(IFormFile file)
{
    var result = await _imageUploadService.UploadImageWithTextWatermarkAsync(file);
    return Ok(result.SecureUrl);
}

💡 Optimization Highlights

Uses System.Drawing for high-quality resizing
Smart logic to scale down large images, skip resizing small ones
Uses JPEG encoding with ImageCodecInfo for compression control
Clean architecture: interface-based service, separated config, reusable watermark logic

🔐 Watermark Configuration

You can easily tweak the watermark style using the WatermarkConfig class:

public class WatermarkConfig
{
    public string Text = "GOORFA.COM";
    public string FontFamily = "Arial";
    public int FontSize = 20;
    public string Color = "#FFFFFF";
    public int Opacity = 50;
    public string Position = "center";
}