Digital collage is the technique of using computer tools in collage creation to encourage chance associations of disparate visual elements and the subsequent transformation of the visual results through the use of electronic media. History of technique of collage started with cubist painter, Pablo Picasso, who invented the collage technique in 1912 with his Still Life with Chair Caning (Nature-morte Ã la chaise cannÃ©e), in which he pasted a patch of oilcloth with a chair-caning design to the canvass of the piece…
Cubomania is a collage made by cutting an image into squares which are then reassembled automatically or at random. Inimage is a name given by RenÃ© Passerson to what is usually considered a style of surrealist collage (though it perhaps qualifies instead as a decollage) in which parts are cut away from an existing image to reveal another image.
Collages produced using a similar, or perhaps identical, method are called etrÃ©cissements by Richard Genovese from a method first explored by Marcel MariÃ«n.
Genovese also introduced excavation collage (that includes elements of decollage) which is the layering of printed images, loosely affixed at the corners and then tearing away bits of the upper layer to reveal images from underneath, thereby introducing a new collage of images. Penelope Rosemont invented some methods of surrealist collage, the prehensilhouette and the landscapade.
Collage was often called the art form of the 20th century, but this was never fully realised.
Surrealist games such as parallel collage use collective techniques of collage making.
Collage made from photographs, or parts of photographs, is called photomontage.
Read more here: http://en.wikipedia.org/wiki/Collage