Tilt shift is pretty easy in Gimp or Photoshop. Take a picture with your subject in the middle, and then seriously blur both the foreground and background. In normal outdoor photographs, due to the distances from the camera, it's very difficult to get both the foreground and background out of focus. But with macro shots of close up objects, you have a narrow depth of field and you do get a lot of blur in the foreground and background. So by artificially blurring the outdoor landscape shots, it fools the eye into thinking it must be a miniature.
