To model in wireframe and still see a reference image, instead of assigning the image to a polygon plane (I think that this is what you have done), you would need to import the image so that you can see it through the relevant camera.

So, go to your viewport menu and select Image plane>Import image. It is a good idea to set the window to default view before doing this.

Not sure if I understood your question correctly, but I hope that this helps.