if you are running your members area on a subdomain like pics.site.com then strongbox will use a sub-sub domain like sdfasdf.pics.site.com

if you want both site.com and pics.site.com protected you may need 2 installs of strongbox and use the secure handoff from one to the other. I assume you are using subdomains for pics because of content sharing? If yes, you should look at using symlinks instead of subdomains.