Based on the website, that image is from WWI, which means it originated sometime between 1914 to 1918. The “youngest” this photo could be is 92 years old, which means it’s copyright period has expired. In the US, copyright protections are granted during the lifetime of the author with a bonus of 70 years after death. That would make this photo copyrighted, maybe. However, this photo was taken before the Copyright Act of 1976, so that might make it okay to use. What you need is the name of the photographer and his (or her?) date of death. You may also want to see if the website of this picture has an image use policy. However, because of the photo’s age, it seems pretty safe to use.