If by algorithm you mean the criteria based on which the selection is made, I'd say the color of the pixels. Gimp has a similar tool called select-by-color, which selects the areas with pixels of identical/similar color.Does anyone know what is the algorithm behind the quick selection tool in adobe photoshop
Thanks man...Here: yuwing.kaist.ac.kr/courses/cs770/reading/grabcut.pdf.
If that's what you're looking for.