To get a media (i.e.: image)  in code-behind you can do it like this.

var currentPage = umbraco.presentation.nodeFactory.Node.GetCurrent();
var media = new umbraco.cms.businesslogic.media.Media(
            Convert.ToInt32(currentPage.GetProperty("[property]").Value)
    );
string imageUrl = media.getProperty("umbracoFile").Value.ToString();