DAZ Studio is used to manipulate 3D models, pose them, dress them, apply hair of different styles etc., and then it can produce a rendered 2D image of whatever is in your scene.
If you are working from a 2D photograph of a person, then you would be much better off using Photoshop or Gimp or similar to manipulate the images, but I am sure you have these already?
There are loads of fantasy items available in the store here for using inside DAZ Studio, like elf costumes, fairy dresses, and even morphs for pointy ears for some of the characters available too. You could use these on their own, or applied to a model like Genesis, and pose them in the way that you want them to appear in your finished image. You would then create a 2D render of your clothing, and you could use that in Photoshop or similar as a new layer.
DAZ Studio does not have the ability to turn 2D images into 3D models if that is what you were thinking, but it could still be a useful part of your workflow?