http://urbanhonking.com/ideasfordozens/2013/01/14/making-photomosaics-in-processing/ - photomosaics and computational-collages
Sideways thinking -- text collages (cf Lewis Warsh). Images made of text, ascii art, &c.
Scattered Letters at Open Processing - not a collage.
If the image is pixellated and a block replaced with something-else of an “equivalent” value (average color, shade, intensity, ascii character based on light/dark, fragment of another image) - that’s a mosaic. If the source is a solid color, it looks more like a “traditional” mosaic. If the source is a (whole) photo - photomosaic. If the source is TEXT then... ??? - Sergio Albiac’s text-collages
http://www.openprocessing.org/sketch/113596 - a changing collage on OP, some of which elements are textual (images) [Hungarian!].
Gastrotypographicalassemblage - Herb Lubalin, Lou Dorfsman 1966