Here is a list of ideas.
1. When you upload a skin, you must click a confirm button first and there it will check the last 50 skins that were posted/updated and if any one of them is a match you will be banned for a day.
2. When posting skins, you must wait 10-30 minutes after the other one you posted. This way even if they do copy, it won't be very efficient. And you are much less likely to have your skin copied.
3. The report button should be changed. It should be if 1-10 different people click it, the skin is deleted and the owner of the skin is automatically sent a message saying, "The skin ____ has been deleted due to a sufficient amount of votes that this was copied. If the same thing happens to 1-5 more of your submissions, you will be banned for one hour-one week." so you get the picture.

If you have any other ideas please post them in the comments and I will try to add them to this list. Please give a diamond if you want 1-3 of these to be implemented into Planetminecraft and tell your friends. Basically do your best to help Planetminecraft become aware of these possibilities. Thanks for your time! :D