I’ve got an Image as Stream coming in and I’m trying to convert the incoming Image from whatever it maybe (even if it already is a PNG) to a PNG.

I’m doing this as part of sanitizing the image as it comes from a source I do not trust.
By converting it I’m trying to get rid of any code that might have been injected into the image before I store it and return it to a frontend client at a later date.

I’m trying to do this in memory and to my knowledge it should be done like this:

Image image = Image.FromStream(stream, false, true);
using (MemoryStream ms = new MemoryStream())
{
    image.Save(ms, ImageFormat.Png);
    return ValidateImage(path, ms);
};

What ive noticed however is that doing it in the above way has a different result from storing the image to disk and then reading it again after ive converted it.

Image image = Image.FromStream(stream, false, true);
using (MemoryStream ms = new MemoryStream())
{
    image.Save(ms, ImageFormat.Png);
    File.WriteAllBytes(path, ms.ToArray());
};

using (FileStream fs = new FileStream(path, FileMode.Open))
{    
    return ValidateImage(path, fs);
};

My ValidateImage method at some point does this:

byte[] bytes;
using (MemoryStream ms = new MemoryStream())
{
     contentStream.CopyTo(ms);
     bytes = ms.ToArray();
}

if(Validate(bytes)){
}

public override bool Validate(byte[] data)
{
    try
    {
        // Try to open the image
        Image img;
        using (Stream ms = new MemoryStream(data))
        {
            img = Image.FromStream(ms);
        }

        // Check if the format matches the expected format
        return img.RawFormat.Equals(_format);
    }
    catch (Exception)
    {
        // Return false on exception
        return false;
    }
}

The above Validate() returns false when I do the conversion solely in memory and I’m wondering why and was hoping to find a sage who could enlighten me and help me to do it properly.

Thank you in advance