There is now a need to associate files with contenttypes.  Take a look at the alloy tech or below code, it needs  a contenttype with teh required extensions

 [ContentType(GUID = "0A89E464-56D4-449F-AEA8-2BF774AB8730")]
    [MediaDescriptor(ExtensionString = "jpg,jpeg,jpe,ico,gif,bmp,png")]
    public class ImageFile : ImageData 
    {
        /// <summary>
        /// Gets or sets the copyright.
        /// </summary>
        /// <value>
        /// The copyright.
        /// </value>
        public virtual string Copyright { get; set; }
    }