When photographing or painting your own textures, it is sometimes desirable to be able to seamlessly tile the image over a surface.

Above we have a photo I took of some corroding metal with flaking paint. The image is clearly good source for a tileable texture.

However, it isn't tileable yet as we see when the image is tiled a few times on a plane. The tile edge is clearly visible in the center of the above image.

So we need to tweak the texture in Photoshop so that it can be tiled. In the image above, we have completed step one which is to use the Filter/Other/Offset tool. If your source image is 256x256, you will enter 128 for both the horizontal and vertical shift. Then click the Wrap Around radio button in the undefined area field. Now the image is tileable, but we can clearly see edges.

You get rid of the edges by playing with the clone tool, as well as doing a little strategic copy/pasting with feathered selections. This gets a little tedious but it works.

So now we're done. We can see how the image cleanly tiles on the surface in the above render.