Need MD5 hash for an in memory System.Drawing.Image

Question

The title says it all.

Answer 1

Here is a basic snippet. See also @JaredReisinger 's comment for some questions.

using System.Security.Cryptography;
using System.Text;
using System.Drawing.Imaging;
// ...

// get the bytes from the image
byte[] bytes = null;
using( MemoryStream ms = new MemoryStream() )
{
    image.Save(ms,ImageFormat.Gif); // gif for example
    bytes =  ms.ToArray();
}

// hash the bytes
MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
byte[] hash = md5.ComputeHash(bytes);

// make a hex string of the hash for display or whatever
StringBuilder sb = new StringBuilder();
foreach (byte b in hash)
{
   sb.Append(b.ToString("x2").ToLower());
} 

Answer 2

A simple sample, based on the sample in MSDN; note that this hash is dependent on the internal representation of the image and will not correspond to the hash created from a file.

using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Security.Cryptography;
using System.Text;

class Program
{
    static string getMd5Hash(byte[] buffer)
    {
        MD5 md5Hasher = MD5.Create();

        byte[] data = md5Hasher.ComputeHash(buffer);

        StringBuilder sBuilder = new StringBuilder();
        for (int i = 0; i < data.Length; i++)
        {
            sBuilder.Append(data[i].ToString("x2"));
        }
        return sBuilder.ToString();
    }

    static byte[] imageToByteArray(Image image)
    {
        MemoryStream ms = new MemoryStream();
        image.Save(ms, ImageFormat.Bmp);
        return ms.ToArray();
    }

    static void Main(string[] args)
    {
        Image image = Image.FromFile(@"C:\tmp\Jellyfish.jpg");
        byte[] buffer = imageToByteArray(image);
        string md5 = getMd5Hash(buffer);
    }
}

To be able to use the MD5 class you need to add a reference to System.Security.

Depending on what you are going to use the hash for you should consider the fact that MD5 is no longer state of the art and that there are better hash functions available if you need a strong hash.

Answer 3

Thanks to the other fellows who answered. Here's what I ended up doing:

MemoryStream ms = new MemoryStream()
image.Save(ms, ImageFormat.Png);
byte[] imgBytes = ms.ToArray();

MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
byte[] hash = md5.ComputeHash(imgBytes);
string imageMD5 = BitConverter.ToString(hash).Replace("-", "").ToLower();
ms.Dispose();