DCT (Crash Barrier)
DCT is a lossy graphics format, and associated software for DOS, developed by Andy Green and Crash Barrier Ltd. As of v1.2 of the software, it is grayscale only, and gives the impression of being experimental.
Based on its name, maybe it uses DCT compression.
DCT files created by DCT Coder 1.2 are observed to start with ASCII "
DcT1.2", followed by
Ed. note: The decoder only displays a DCT image, with no option to convert it to another format. The software seems to be very picky about a number of things. To confirm that it does do something, test it with a GIF87 image no more than 320x200 pixels in size, with a light-colored background.