Here is a collection of photos from the World War I era (1914-1919 or so). Most of them are from Europe, and show soldiers on both sides of the fight who have formed impromptu bands, which include at least a couple of homemade/handmade instruments. In addition to box guitars and other oddities, a favorite of the time appear to be longer-scale cello-like instruments, having a tin can resonators (Hugo informs us this is likely a “Vozembouch”, a traditional Czech instrument – see comments below).