I have used the following code in an itemAdded event receiver.

            public override void ItemAdded(SPItemEventProperties properties)
            {
                if (properties.ListTitle == "Architecture Calendar")
                {
    
                    base.ItemAdded(properties);
                    string eventUrl = null;
                    string AttachUrl=null;
    
                    using (SPSite site = properties.OpenSite())
                    {
                        using (SPWeb web = site.OpenWeb())
                        {
                            try
                            {
                                SPList listCalendar = web.Lists[properties.ListId];
                                SPItem itemCalendar = properties.ListItem;
                                SPSite mainSite = new SPSite(site.Url + @"/admin/");
                                SPWeb mainWeb = mainSite.OpenWeb();
                                
                                **AttachUrl = properties.ListItem.Attachments.UrlPrefix + properties.ListItem.Attachments[0];**
    
                                SPList listIntegrated = mainWeb.Lists["IntegratedEvents"];
                                SPListItem itemIntegrated = listIntegrated.Items.Add();
    
                                **itemIntegrated["Picture"] = AttachUrl;**
                               
                                
    
                                itemIntegrated.Update();
                                
    
                            }
                            catch (Exception Ex)
                            {
                                throw Ex;
                            }
                        }
                    }
                }