I am asking this question purely our of curiosity. I do not look for step-by-step tutorial on how to manipulate a photo and making sure that it will be hard to detect it.
I was wondering, because tools like http://fotoforensics.com/ make it easy to detect modifications of photographs in software like Photoshop. I can see that it is based on things like Error Level Analysis. Is there a way to modify a photo but "cover the tracks" so there will be no easy way of detecting modifications by "ELA" or other metods? Is it hard, easy to do? Is it widely used?