in reply to CGI gnuplot via system command

If I interpret your (not very well formattted) post correctly, the browser shows postscript source code.

I don't think that most browsers handle that in a meaningful way, so I'd recommend switching to PNG and sending the appropriate content-type.

Or maybe your problem is deeper, and you're trying to send image data and HTML in a single request? Without seeing more of your code that's hard to tell.