Gimp-texturize is a plug-in for the GIMP, a famous picture editor and
 manipulator.
 .
 A few images are designed to be copy-pasted one next to another and still
 look natural, but the result is usually periodic and very monotonous. The
 Texturize plugin allows you to have a realistic pseudo-periodicity.
 .
 After install, the plugin will be available at Filters > Map > Texturize.