Custom camo and 3D models

Hello. I have a question to people who make custom camouflages. I’ve seen some users that included a 3D render image (in Blender for example) of a tank with their camo. And I’m wondering if they made these models themselfes and just adjusted the UV map to the texture or they did it in a different way. I’m asking because I’m making a tank model and i wanted to adjust already existed texture to the model and then so i can either make new camo easier or add any camo i want. The problem with this is that these textures have a lot of elements and guesing everyone of them where they belong is kind of a pain so I’m not sure if they do it this way. I’ll be thankfull for any helpful informations.