Autostereogram is a 3D image that can be seen without any other tools. However this pattern won't reveal itself unless you stop focusing on the picture and let your look pass the surface to somewhere beyond it. The repeated columns in the image will help your brain to find this focus point.
Read more about autostereogram images

Screen

1. Open the image in full screen mode.
2. Make sure the distance between your eyes and the screen is somewhere between one ft. and two.
3. Try to find the reflection of your face in the screen, imagine you are watching yourself in a mirror.
4. Keep focused on your eyes, don't focus back on the image.
5. Very slowly move back and forth inside the range of one ft. and two.
6. Continue your slow motion until you see the pattern pops up from background in the image.
7. Shift your focus from your eyes to the pattern.
8. If you lost the pattern, focus back on your eyes and repeat the steps above.
9. Wait for a short time so your eyes will lock on the pattern.
10. Enjoy watching 3D!

Paper

1. Keep the picture down in your hands.
2. Look at a small object two ft. away from your eyes.
3. Slowly bring the picture up.
4. Stop where it is going to cover the object you are looking at.
5. While keeping your focus on the object, use your peripheral vision to see the picture.
6. Very slowly move the picture back and forth.
7. Continue moving picture slowly until you see the pattern pops up from background in the picture.
8. Shift your focus from the object to the pattern.
9. If you lost the pattern, focus back on the object and repeat the steps above.
10. Wait for a short time so your eyes will lock on the pattern.
11. Enjoy watching 3D!