Media picMedia = new Media(imageId);Or you can do this easily with :
Image.ImageUrl = picMedia.getProperty("umbracoFile").Value.ToString();
public static string GetImageByID(int imageId)
{
string returnImage = "";
if (imageId != null)
returnImage = (new umbraco.cms.businesslogic.media.Media(imageId).getProperty("umbracoFile").Value).ToString();
return returnImage;
}