Pull off at least four medium sized chunks of adhesive putty -- one for each corner of the poster. If your poster is large or made of heavier paper, pull off a few more chunks to add on the sides as extra reinforcement.
Roll the pieces between your hands to form them into small balls.
Lay the poster facedown on the floor or flat work surface, and then gently stick the balls to the back of the poster. Stick one ball in each corner, and then add any additional balls along the edges to help hold up the poster.
Align the poster against your wall where you want to display it. Make sure it is straight, and then press the poster firmly against the wall. Use your index finger to push the corners of the poster, so the balls of adhesive putty flatten against the wall.
Repeat this process to add more posters around the room, if desired, in carefully selected locations. Give the poster enough space on all sides so it is the focal point of the room, or group it together with other posters. If you choose to group your posters, make sure to space them evenly.