Ostenson, De Kalb, Illinois

I have a couple of old family photos, one from studio J.O. Oleson in De Kalb, Ill: of a family, parents and two young women ca. 1900. Another photo of the parents sitting outside their farm building. Written on the back 'Olli Østhenson', probably Ole Østensen. No clues so far, I am on the point of giving up. Key words: Norwegian immigrants from Ryfylke, Norway, perhaps Suldal or Sand since they were sent to family members in this area. But no immigrants from this area fit so far. Strangely enough the studio 'J.O. Oleson, Photographer, De Kalb, Illinois' does not turn up in a general web search. Grateful for clues or hints or any ideas. Tusen takk.