I did some quick researching:
National Defense Service Medal Criteria: It is awarded for honorable active military service as a member of the armed forces of the United States including the Coast Guard, between June 27, 1950 and July 27, 1954, (Korean War), between Jan. 1, 1961 and Aug. 14, 1974, (Vietnam War), between Aug. 2, 1990 to Nov. 30, 1995 (operations Desert Shield and Desert Storm), and currently from Sept. 11, 2001 to a date to be determined (terrorism attacks on the United States). Service members who earned the medal during the first qualifying period, and who again became entitled to the medal, wear a bronze star on the ribbon to denote the second award of the medal.
Global War On Terrorism: To receive the Global War on Terrorism Service Medal, a military service member must perform duty in a designated anti-terrorism operation for a period of either 30 consecutive or 60 non-consecutive days of duty. For those who were engaged in combat, killed, or wounded in the line of duty the time requirement is waived
Army Service Ribbon: The Army Service Ribbon is awarded to members of the Army, Army Reserve, and Army National Guard for successful completion of initial-entry training, which for officers is considered to be successful completion of their basic/orientation or higher level course.
NDSM requires active service, GWOT requires support of an anti-terror mission for the time period stated. I don't think there's a single ribbon you can pin on.
While *anyone* can wear any military uniform, it's actually illegal to wear ribbons you haven't earned. I recall the story of a marine who went around a community telling everyone he won all sorts of medals in combat (that he didn't earn) and was subsequently prosecuted. I'm not saying you'd do that, but people (like myself) do pay attention to ribbon racks and what's on them. I can't advice you to put on ribbons for a portrait and tell you everything is going to be ok, so tread carefully.