A set of pictures, which can be placed one next to the other, many times both horizonatally and vertically and would blend
together (the edges would not be noticed since the pattern
of a tile continues naturally in the next tile).
A simple trick to create seamless tiles:
- Duplicate the layer containing the background tile.
- Flip the duplicated layer horizontally / vertically.
- Make sure the duplicated layer gradually goes from full opacity to transparency (use a soft-tip eraser, apply a mask to the layer with a gradient etc.).
Result: The tile will gradually transform into its own "mirror" title. Since an image and its mirror image are smoothly connected, the edges would seamlessly continue.