Did you UV Map the object?
If not, then an image file wont work properly on it. You need to create a UV Map in something like UV Mapper or similar (free version), create a texture template, save the OBJ, load the template into Photoshop (or similar), colour in the template, save it, then load it into DS4 via the Diffuse channel in the Surfaces tab.
You can also create Bump, Displacement and Reflection maps the same way.
That is the gist of it. If you need more help, I am sure we could go into it a bit more for you.