It's just a CNAME to an akamai IP:

    $ host captcha.nsa.gov
    captcha.nsa.gov is an alias for www.nsa.gov.edgekey.net.
    www.nsa.gov.edgekey.net is an alias for e6655.dscna.akamaiedge.net.
    e6655.dscna.akamaiedge.net has address 104.75.125.118
    e6655.dscna.akamaiedge.net has IPv6 address 2600:1406:5800:7b5::19ff
    e6655.dscna.akamaiedge.net has IPv6 address 2600:1406:5800:792::19ff

edgekey.net is an akamai thingy, all of nsa.gov seems to go through it

    $ host www.nsa.gov
    www.nsa.gov is an alias for nsa.gov.edgekey.net.
    nsa.gov.edgekey.net is an alias for e16248.dscb.akamaiedge.net.