A "commissioned photograph" is one that has been taken for a specific client under a specific contract. For example, if a couple hires a photographer to take pictures at their wedding, those are commissioned photographs. "Non-commissioned photographs" are those a photographer takes on his or her own, usually with the intent to sell them later to whoever will buy them.
That said, I don't think there is an easy translation for "non-commissioned" in this context. "Non-commissioned international picture markets" could probably be translated something like "mercados internacionales de las fotografías tomadas sin contrato" but I don't know how awkward that is.