The coolest method of seamless tiling is what I refer to as "perpetuating repetition" or Perpetual, because when it is tiled, the image seems to be perpetual, going on and on indefinitely in all directions, not mirrored or overlapped. This is also the most timestaking technique, although the directions are deceptively brief. This method does require artistic skill and familiarity with your paint program, although those who don't feel very artistic can probably still create something decent by working with a very simple image. The more complex the original is, the more involved the process becomes.

Cut a portion vertically from the right and move it to the left side.

Modify the original edge by blending, cloning or inventing portions of the graphic until no seam is visible.

Select this image to see its tiled appearance.