Why does /opt/local/bin/captoinfo already exist and not belong to a registered port? Did you have MacPorts installed before, and uninstalled it incompletely, and then reinstall it? Or perhaps you installed third-party software that was itself built with MacPorts and installed itself into the MacPorts prefix? Either way, you can either force the installation with -f like the error message says, or if you cannot explain how /opt/local/bin/captoinfo got onto your system, then you may have other unregistered files on your system which will cause you the same problem in the future, in which case it might be simplest to uninstall MacPorts and all ports properly, and then reinstall MacPorts.
