Usiing CON as the filename will only get the output to the command line. To capture it into the program you should use open instead. Something like

open IN, "echo $script | $program |" or die $!;
binmode IN;
my $img = do{ local $/; <IN> };
close IN;
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See perlopentut for the details of grabing program output using open. This is necessary as you will need to use binmode to prevent the stream being interupted by ^Z.

If I do this MyPerl.PL > plot.jpeg, isn't this script

`echo $script | $program`;
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and this script

open IN, "echo $script | $program |";
binmode IN;
my $img = do{ local $/; <IN> };
close IN;

binmode STDOUT;
print $img;
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the same? In any case, the jpeg produced was always something of a dozen bytes size or so, certainly not jpeg.

Since the binmode, open and all technique works with GD, I wonder if that external program simply somehow fails to generate a jpeg properly with CON as filename. Just afraid to waste people time if the problem is totally exogenous to Perl.

Thanks for bearning with me.