Recent XTerm versions are capable of displaying Sixel graphics, a format supported by terminals and printers from DEC. These are displayed when a stream of Sixel characters are sent to the screen e.g. using "cat" under Unix (or "TYPE" under VMS using the DECWindows terminal).
The attached patch adds code to the "tek.trm" driver so that Sixel character streams may be created and images appear between Gnuplot command line prompts (so not in a separate window).
Gnuplot has to be compiled/configured with the "--with-bitmap-terminals" option.
XTerm has to be compiled/configured with "--enable-sixel-graphics", and started with "-ti 340" on the command line to specify a Sixel capable terminal. Furthermore, the menu option "sixelScrolling" should be checked; foreground black and background white.