If you allowed users to upload their own images, and those images were of Mickey Mouse, and you printed them and sold them, Disney would have a pretty easy claim against you.
You're not just selling a neutral tool here, you're actually printing the potentially infringing art.
> Also there is no way knowing whether I sold any mickey mouse shirts.
Think this statement through. I can come up with a couple of ways for a rights-holder to figure out if you're selling merchandise that infringes on their marks. They can attempt to order one themselves. They can see a tweet where someone shares the cool t-shirt they bought from you.
You're probably not actually in much danger here, but I would still take the hazard seriously if I were you. Be careful.
Currently, I review all created designs before printing, so that would be a way of not infringing, I. E. Cancel orders which are potentially infringing
Indeed. Here is an example of a company ordering trademark-infringing goods directly from a vendor, then successfully pursuing legal action against that vendor:
You're not just selling a neutral tool here, you're actually printing the potentially infringing art.
> Also there is no way knowing whether I sold any mickey mouse shirts.
Think this statement through. I can come up with a couple of ways for a rights-holder to figure out if you're selling merchandise that infringes on their marks. They can attempt to order one themselves. They can see a tweet where someone shares the cool t-shirt they bought from you.
You're probably not actually in much danger here, but I would still take the hazard seriously if I were you. Be careful.