The GNU Image Manipulation Program (GIMP) has tools for tasks such as photo retouching and image composition.
Used when digitising a Spanish 18th century account book: Keating, J., Teehan, A., Gallagher, D., & O'Connor, T. (2010). A digital edition of a Spanish 18th century account book: user driven digitisation. Jahrbuch für Computerphilologie, 10, 169-18.
Professional quality cross-platform vector graphics software for creating and editing a wide variety of graphics such as illustrations, icons, logos, diagrams, maps, and web graphics.
Used by Oxford Archaeology for processing archaeology data: Hodgkinson, A., Bianconi, L. & Costa, S. (2013.) Open source GIS for archaeological data: two case studies from British and Egyptian Archaeology. In G. Earl, T. Sly, A. Chrysanthi, P. Murrieta-Flores, C. Papadopoulos, I. Romanowska & D. Wheatley (Eds.), Archaeology in the digital era: e-papers from the 40th conference on computer applications and quantitative methods in archaeology (CAA), Southampton, 26-30 March 2012 (Volume II, pp. 742-751). Amsterdam: Amsterdam University Press.