For make a realistic addon, it's necesary to take real photos, but it needs a hard edition for do a professional addon.
The Lx_seat.dds, for example, it's necesary about 5 hours to make good proportions and do, from scratch, the light effects to be convincing. In this case I took a real photo. Well, and make the perfect implementation of the texture/photo on the dds file because there are limits on dds file (for example, holes in the seat,etc).
Normally, in all my addons, the lightning effects is made from scratch almost always. Example: Tyre tread pattern from Revolution Pack April 7th (even de 3D effect, of course).
In other cases, it is necessary to implement in the same texture, different parts of different photographs. Sometimes it is necessary to make items from scratch and implement them, too.