Now why others must steal the skin, make something to make private!!

Don't use it online then... That's the solution. In order for other people to see it, it has to be downloaded from somewhere. It's public if you want it to be displayed and thats not possible to hide.

Admitedly, not the solution you want, but it's exactly the same with layouts - if used on public server, easy enough to copy when you join.

You could do one thing to prevent it but do not !! for example the entry "You want to publicize the skins? and you could decide to keep the skin private!

If you want other players to be able to see your skin, then it has to be sent to the client. If it's sent to the client, it can be 'stolen'.

This is not a matter of knowledge or coding or effort, it is just logic. Your LFS client can't paint it onto a car unless it has the data, and if it has the data, then no matter how much protection Scawen puts in to hiding it, there will always be someone who is able to get that data out of LFS and back into an image.

Look at setups - they're protected, but they have to be included in replay files in order for the replay to be smooth. They're encrypted and Scawen didn't advertise their presence, but someone found them, figured out the encryption and wrote a setup extractor. Now those in-the-know can get the setup of anyone they're online with or have a replay of.

Aight, so our boy here made a skin, and makes a post on the forums because his skin got stolen by someone that, deep in his heart, he gives no damn about and will have forgotten in 2 weeks tops. Talk about crying out loud.
I make skins too. Most of them are private. I've only seen 1 of my skin ever being stolen, and I couldn't care less. Other people aren't supposed to use it, but to every bad thing there's a good side; ying and yang. Someone found my skin cool enough to try to get it for himself. It's a selfish act but also an act of recognition to my work, which I appreciate at least a minimum. End of the story.
Oh and did I mention that you can't download skins in any higher resolution than 1024p, which completely ruins it for highly-detailed skins? That person's stealing is absurd, and so is your post, both morally and logically (as others have explained) speaking. Go cry elsewhere please.