If you would like to make and submit a spoiler image to be used for a specific tag, please use this thread for it. There is only one requirement which is to be consistent. We would like all of them to have the same border or the same font text. That will probably be decided by the first one we choose so please follow that example.
As for the selection process, we don't want to overly complicate something so simple. We'll use it if it's well designed, consistent and we like it, then give the creator an exclusive badge for it.
We look forward to your submissions.