Once the poster is creased or wrinkled, there will probably always be some indication that it has been folded. If you use one of the following methods to remove poster creases, be careful and you should see results. Always take expensive posters and artwork to an expert.
Fold the poster gently in the opposite direction along the creases. Then weigh the poster down and lay it flat for a few days.
Hang the poster in a humid spot for a couple of days. The bathroom is the most humid spot in most houses. Use clothespins or plastic-coated clips to suspend the poster from a temporary clothesline.
Lay the poster facedown on a flat surface. Cover it with another piece of heavy paper. Carefully iron the poster through the heavy paper and check frequently to make sure you're not burning the poster, or causing discolouration.
Have your poster laminated if the creases are severe. The laminate will hide most of the flaws.
Dry mount the photo with dry mount tissue paper, or have a professional with the right equipment do this for you. Tissue paper is placed between a backing and the photo, and carefully ironed until the adhesive melts. A professional uses a press to do this, but you can do it at home.
Use spray-on adhesive to affix the poster to a backing. Spray the adhesive on foam board and then lay the poster on top. Gently spread out any wrinkles or creases.
Roll posters and store in poster tubes.
Don't use these methods on expensive posters.