Nope, unfortuantly there isn't a way to select the cars you race against yet that I know of. What you can do though is photoshop the image to contain the cars you want.
i dont think you can do this, but i can think of something which is going to get you near enugh. choose a race in arcade mode and choose your car etc etc and usually the cars are pretty similer (same catagory) as yours and just save the replay then REPLAY it and take pics, sorry if this dont help lol