Images taken by Sony DSC-W200 camera are only 72 DPI.

Pictures on a digital storage don't have any DPI. You get DPI when feeding the pictures into an output device, that is, you can put a ruler on it and measure it. Unfortunately JPG does have DPI tags. I don't know, what these tags try to tell us. With tag editors any value can be put into these tags without any visible effect. Non-displayed pictures are measured in Pixels (width x height).

Initialize camera by going to Menu settings, that will reset camera to default settings and problem will solve.