Example?? You find it by every video or foto gallery!! Youtube, googlevideo, dailymotion also by non famous galleries.
I will explain:
We have 3 images in the gallery:
Image1 (Keywords: Mercedes, bmw)
Image2 (Keywords: Mecedes, Honda)
Image3 (Keywords: Ferrari, Opel)
Ok, when you view the Image1
(Keywords: Mercedes, bmw) you get onder the related image (By KEYWORDS): Image2
(Keywords: Mecedes, Honda) because:
The keyword
MERCEDES of image1 is also the keyword of the image2
I hope I did a good explain