The advances in photography made it even more common for pictures to be taken. The World War I Victory medal, awarded to all members of the American Military. And perhaps you found an oval disk such as this, scratched and worn. This is the origin of the dogtags we are more familiar with. I was truly a global war, raging across Europe and pulling in troops from countries throughout the British Empire and America.
Many countries have web sites with histories, photographs and documents.
I Document Archive contains many documents associated with the war. It also is an excellant starting point for useful links across the world. It includes a Biographical section and remembrances of key persons involved. Several continue to exist and their publications can be excellent sources of overall historical information, though they may not go into individual information. Among those organizations was the American Legion, founded in 1919.