The term collage derives from the French “colle” meaning “glue “.  This term was coined by both Georges Braque and Pablo Picasso in the beginning of the 20th century when collage became a distinctive part of modern art . 
According to the Guggenheim Museum ‘s online art glossary, collage is an artistic concept associated with the beginnings of modernism, and entails much more than the idea of gluing something onto something else. The glued-on patches which Braque and Picasso added to their canvases offered a new perspective on painting when the patches “collided with the surface plane of the painting.”  In this perspective, collage was part of a methodical reexamination of the relation between painting and sculpture, and these new works “gave each medium some of the characteristics of the other,” according to the Guggenheim essay. Furthermore, these chopped-up bits of newspaper introduced fragments of externally referenced meaning into the collision: “References to current events, such as the war in the Balkans, and to popular culture enriched the content of their art.” This juxtaposition of signifiers, “at once serious and tongue-in-cheek,” was fundamental to the inspiration behind collage: “Emphasizing concept and process over end product, collage has brought the incongruous into meaningful congress with the ordinary.”
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 . It is commonly used in the creation of digital art .
The concept of collage has crossed the boundaries of visual arts. In music , with the advances on recording technology, avant-garde artists started experimenting with cutting and pasting since the middle of the twentieth century.
In the 1960s, George Martin created collages of recordings while producing the records of The Beatles . In 1967 Pop artist Peter Blake made the collage for the cover of the Beatles seminal album Sgt. Pepper’s Lonely Hearts Club Band . In the 1970s and ’80s, the likes of Christian Marclay and the group Negativland reappropriated old audio in new ways. By the 1990s and 2000s, with the popularity of the sampler , it became apparent that “musical collages ” had become the norm for popular music , especially in rap , hip-hop and electronic music .  In 1996, DJ Shadow released the groundbreaking album, Endtroducing….. , made entirely of preexisting recorded material mixed together in audible collage. In the same year, New York City based artist, writer, and musician, Paul D. Miller aka DJ Spooky ‘s work pushed the work of sampling into a museum and gallery context as an art practice that combined DJ culture’s obsession with archival materials as sound sources on his album “Songs of a Dead Dreamer” and in his books “Rhythm Science ” (2004) and “Sound Unbound (2008)” (MIT Press). In his books, “mash-up” and collage based mixes of authors, artists, and musicians such as Antonin Artaud , James Joyce , William S. Burroughs , and Raymond Scott were featured as part of a what he called “literature of sound.” In 2000, The Avalanches released Since I Left You , a musical collage consisting of approximately 3,500 musical sources (i.e., samples). 
Exhibition of traditional and digital collage by many artists – curated by Jonathan Talbot in 2001
collageart.org , A website dedicated to the art of collage
Franz Kafka, Marcel Proust and Alfred Hitchcock, the 3 Albums , “recomposed photographs”, in a rather surrealist spirit
Sound Unbound: Sampling Digital Music and Culture. Edited by Paul D. Miller aka DJ Spooky that Subliminal Kid. Foreword by Cory Doctorow . Introduction by Steve Reich▪ Rhythm Science The conceptual artist Paul Miller, also known as DJ Spooky delivers a manifesto for rhythm science—the creation of art from the flow of patterns in sound and culture, “the changing same.”