Collage shortcuts

Is it defendable using pictures made by others? Luckily, legislation defines the final art work as creation without any obligation to its sources. So don't bother about it, just go
My own justification is the transitory character of the pictures which are my raw material. There is a growing tendency to protect everything in order to obtain royalties, but I am against it. Art cannot exist without freedom and without exchanges between artists – dead or alive. Bach is a famous example for his “borrowings” (his transcriptions), Picasso for his variations on famous paintings. Or in more recent times L.Berio and his musical collages.
Another question concerns meme hacking. For me, perverting a work of art shows its stereotypes or refreshes the work which is weakened by overreproduction. Anyway, the original remains visible in the new collage but gains a new meaning. Here it is the perversion of a painting celebrating the king of France.

Another example is my former streetwork, when I was working on billboards in Geneva/
This work was very exciting and was not motived by political reasons, but for sport and fun. I loved the work on big sized posters. I learned by this work to let my works go, as they remained on the board for a couple of days only.As for the pictures displayed on my site, they are free of copyright.Because I want to share them. Their resolution is unsufficient to make orginal-like reproductions. I hate art sites with watermarks on the pictures. Either you show them or you don't.

For me, there are two kinds of collages: illustration and construction.
Illustration is the most widespread kind. Techniques:
You simply insert some alien element in a picture - for ex. you take a diver and put him into a normal landscape;
you make changements in scale, like a giant insect etc.;
you put things upside down.
Generally, in this kind of picture, you have a relatively coherent space (cf. surrealistic pictures).

Construction has to do with edges and rimes. It's about assembling forms and thus create new associations, like in composed words. I usually speak of grafts. Techniques:
you assemble different items while paying attention to their borders;
you work with "rimes", repetition of forms from different objects.
With this kind of collage, you necessarily distort the pictorial space. For the onlooker, it means that he has to decide which form he will privilege, because the relationship between subject and background ist disturbed.
What's the interest in disturbing the poor onlooker, already disturbed by contemporary art?
Because of the conventional aspect of illustration, which - at least in my eyes - comforts the onlooker in his way of seeing. Whereas for me collage wants to change the ways of seeing, as all great art has always done. Not for mere provocation, but in order to open new mental spaces. The danger in doing it is to confuse the onlooker too much, like in conceptual art for ex. Here is the strength of magazine collage: the material is already familiar, it's the cut&and assemblage which makes is alien.