Any way to prevent the Postnet sticker from ending up on the front of a postcard?

When you mail a postcard, sometimes the Post Office will put the postnet sticker on the front of the postcard instead of on the back where the writing is. Is there any way to prevent the sticker from ending up on the front? I like to send puzzle postcards, but sometimes the sticker goes on front and covers up part of the picture side. I called the Post Office and asked them, but they were no help (surprise!).

Spend the extra postage and mail it in an envelope.

I don’t receive many picture postcards these days, but I often get those stickers on magazines. I find they peel off easily with no damage to the underlying document. So it shouldn’t be a big deal, even if they do cover some of the picture.

I haven’t had much luck peeling these stickers off without damaging the underlying image. Here’s an example of the sticker from a postsecret.

I was at the Post Office to drop off some letters and asked the clerk why the sticker sometimes ended up on front. She didn’t know for sure, but she thought they might put the sticker on the front if there’s not room on the writing side of the postcard for the barcode. She said to leave the bottom area clear below the address and that might help ensure the barcode stays on the back.