Gyanítom, hogy a magyar "előkép" kifejezés nem más, mint az angol eredeti tükörfordítása. Írják egybe is (preimage) és kötőjellel is (pre-image).
"előkép (főnév)
1. Utánzásra szánt festmény, kép.
2. Átvitt értelemben: Utánzási példaképen felmutatott személy, vagy dolog."
http://wikiszotar.hu/wiki/magyar_ertelmezo_szotar/Előkép

"As with most of her works, the *pre-image* of these was a photograph. Apart from thematising the artistic micro-world, in this case, the author does not apply her typical strategy of transfer of photography into hyperrealist painting, but rather captures the atmosphere of the event, where viewers communicating with the exhibited artworks (and resting) play an important role."
http://nitrianskagaleria.sk/virtualna-galeria/veronika-srama...

"Around the image, other images, blending or not in one visual continuum, constitute its coimage and influence its interpretation otherwise, it will be perceived and interpreted in respect to other images, to the topos acting as coimage, *preimage*, interimagery, subimage, etc. This is neither semantic pickiness nor hypocrisy, but rather an attempt to distinguish what is not reducible to the text model (even if this is metaphorically stretched to its expressive extremes). (...) If this does not happen and we interpret how successful the restoration is, we actually accept that the restored image is a pretext/*preimage*. The semiotics of forgery deals precisely with this subject."
http://www.nadin.ws/archives/85

"For Bergson, the scheme is not simply a hollow structure, or a *pre-image* - a blueprint for the image - but an "idea" that is different by kind and not just by degree. Further, this idea is dynamic. The interaction between scheme and image is fundamental to this dynamism."
http://www.faculty.umb.edu/gary_zabel/Courses/Spinoza/Texts/...

Modernebb vonatkozásban:
"When the *pre-image* (a wireframe sketch usually) is complete, rendering is used, which adds in bitmap textures or procedural textures, lights, bump mapping and relative position to other objects. The result is a completed image the consumer or intended viewer sees."
http://www.answers.com/topic/rendering-computer-graphics