I have some doubts about the identification on this image, not because it appears other than an 1848 daguerreotype, but because I could not find an O W Marshall to match the data provided by the inscription.
The case of this image is clearly marked: O W Marshall, taken at Spring Valley, Ohio in 1848, age 20. The age could be 23, but on enlargement it looks more like 20.
The problem begins with ‘Spring Valley’ — there are four such locations in Ohio, one each in Geauga, Guernsey, Lucas and Greene counties. I searched the 1850 census (just two years after the image was taken) for O W Marshall in any of those four counties. The only one I found was Oscar W Marshall in Xenia, Greene county, Ohio (which is only a few miles from Spring Valley). Problem is he was only 12 years old in 1850. I find him listed again in 1860 and 1870, and the dates are approximately the same. Clearly too young to be the subject of this photo.
That is if the date and identification are correct. The date certainly seems reasonable. The case has no preserver. The gentleman has a high collar and upswept shoulder-line. The hair is bell shaped. The vest is open, and different material from the coat. All of that is typical of 1848, though most of those features might equally be seen a couple years earlier or later.
The subject certainly looks closer to 20 years old than to 10. But is he O W Marshall? Or did someone write in the identification years later, mistaking this gent for Oscar?
We could find no daguerreian artist active in any of the Spring Valley’s in Ohio. There was one in nearby Xenia (where Oscar W Marshall lived) in 1850: J C Thorp (born ca 1827 in Kentucky). It would be no great stretch to imagine he was there in 1848, though we have no evidence for or against that hypothesis. Or the photographer could have been an itinerant.
Or perhaps the O W Marshall shown in the photo left the area before 1850, or came from somewhere else and was just visiting when he had his picture taken. In any case, this one I have not been able to confirm the inscription, but I find it plausible none the less.

