Better use the NetPBM and jpegtools (see Aminet) command lines then. You will need about 30 MB of ram and temporary space on your HD. Using PIPE:
would also work, but memory might be tight.
Use ilbmtoppm to convert the image into ppm:
ilbmtoppm yourfile.iff >yourfile.ppm
The convert the image into jpeg:
cjpeg -dct float -optimize -quality 90 yourfile.ppm yourfile.jpg
Depending on the version of cjpeg, you might also
need to use a std redirection for the target file (">yourfile.jpg").
I think cjpeg also allows the scaling of the image, but I'm not too sure. djpeg allows it for sure, so for creating a smaller version:
djpeg -dct float -scale 1/8 yourfile.jpg yourfile2.ppm
cjpeg -dct float -optimize -quality 70 yourfile2.ppm small.jpg
You get the picture...
