cjpeg which will convert to JPEG from GIF
Unfortunately it doesn't seem to anymore, the manpage says:
The currently supported input file formats are: PPM (PBMPLUS color format), PGM (PBMPLUS gray-scale format), BMP, Targa, and RLE (Utah Raster Toolkit format). (RLE is supported only if the URT library is available.)
Version 6 of 1995 still seems to be able to do it.
To be a bit more precise about my task, I am working on a component of a CMS/shop system that should be able to run on servers of various web hosters. To get administrative rights would be one thing, but too expensive for the average user of our cms.
It seems most hosters use image libraries without GIF support because of licensing issues?