### Call PhotoDNA REST API

Source: https://www.microsoft.com/en-us/photodna/documentation

Sample code demonstrating how to call the PhotoDNA REST API using a subscription key to validate images against a hash set. This is typically used after onboarding to the service.

```csharp
using System;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text;
using System.Threading.Tasks;

public class PhotoDNAClient
{
    private readonly HttpClient _client;
    private readonly string _apiKey;

    public PhotoDNAClient(string apiKey)
    {
        _client = new HttpClient();
        _apiKey = apiKey;
        _client.BaseAddress = new Uri("https://api.example.com/photodna/"); // Replace with actual API endpoint
        _client.DefaultRequestHeaders.Accept.Clear();
        _client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
        _client.DefaultRequestHeaders.Add("Ocp-Apim-Subscription-Key", _apiKey);
    }

    public async Task<string> ValidateImageAsync(string imageUrl)
    {
        try
        {
            var requestBody = new { imageUrl = imageUrl };
            var jsonBody = Newtonsoft.Json.JsonConvert.SerializeObject(requestBody);
            var content = new StringContent(jsonBody, Encoding.UTF8, "application/json");

            HttpResponseMessage response = await _client.PostAsync("validate", content);
            response.EnsureSuccessStatusCode(); // Throw if not 2xx

            return await response.Content.ReadAsStringAsync();
        }
        catch (HttpRequestException e)
        {
            Console.WriteLine($"Error calling PhotoDNA API: {e.Message}");
            return null;
        }
    }

    public async Task<string> ValidateImageBytesAsync(byte[] imageBytes)
    {
        try
        {
            var content = new ByteArrayContent(imageBytes);
            content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");

            HttpResponseMessage response = await _client.PostAsync("validate/bytes", content);
            response.EnsureSuccessStatusCode(); // Throw if not 2xx

            return await response.Content.ReadAsStringAsync();
        }
        catch (HttpRequestException e)
        {
            Console.WriteLine($"Error calling PhotoDNA API: {e.Message}");
            return null;
        }
    }

    // Example usage:
    // public static async Task Main(string[] args)
    // {
    //     string apiKey = "YOUR_SUBSCRIPTION_KEY";
    //     var client = new PhotoDNAClient(apiKey);
    //
    //     // Validate by URL
    //     string imageUrl = "http://example.com/image.jpg";
    //     string resultUrl = await client.ValidateImageAsync(imageUrl);
    //     Console.WriteLine($"Validation result (URL): {resultUrl}");
    //
    //     // Validate by bytes
    //     byte[] imageBytes = System.IO.File.ReadAllBytes("path/to/your/image.jpg");
    //     string resultBytes = await client.ValidateImageBytesAsync(imageBytes);
    //     Console.WriteLine($"Validation result (Bytes): {resultBytes}");
    // }
}

```

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