Asp.net Security - Validating Uploaded Image File Format

I found two really good links talking about how to upload image file and validate file format in more secure way rather than just checking file extension.

• http://www.dotnetexpertguide.com/2011/05/validate-uploaded-image-content-in.html
• http://www.aaronstannard.com/post/2011/06/24/How-to-Securely-Verify-and-Validate-Image-Uploads-in-ASPNET-and-ASPNET-MVC.aspx

You should also check image file content before you try checking for header of image file.

I found both the articles have missed this code.  Here is that missing code for validating file extension.

private Boolean CheckFileType()
        {
            string[] acceptedTypes = new string[]
            {
                "image/bmp",
                "image/jpeg",                
                "image/gif",
                "image/png"
            };

            if (!acceptedTypes.Contains(fuPhoto1.PostedFile.ContentType))
            {
                return false;
            }
            else
            {
                return true;
            }
        }


Note: This article is basically bookmark for my future reference.