I think you have noticed that the part containing data on a CDR reflects the light differently than the part without data which I think made you ask your question.

The problem is that usual burners are not made for burning only to specified places on the disc while leaving other places free - classic burning means starting in the innermost part of the disc and burning until all the data is written or until eventually the outermost part is reached.

Burning images however means to switch on the laser and switch it off again - which usual burners are not made for (at least that's how I understand all this).

Apart from that, you'll need a special software to calculate which parts of the disc need the laser to be switched on and which parts of the disc need it to be switched off. And I've never heard of such a tool - as I said before, I doubt that it's even possible to do so which might be an explanation for why there is no such tool.

I hope this helps you understand this a bit better (although it is not technically exact at all... )