Using plots for points in gnuplot
Another option is to find a font tingbat font with a suitable glyph. Then you can use "plot with labels" using this symbol as the label string. See for example 5th plot in demo http://gnuplot.sourceforge.net/demo/stringvar.html
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I haven't played with this function at all, but there is:
http://gnuplot.sourceforge.net/demo/barchart_art.html
Which shows the use of png files on a histogram (note that this feature was added in Gnuplot 4.5 - I think). With a little creativity, it seems like you can use this function to do what you ask, although it would require a whole bunch of plot commands to do so, so it would be helpful to write a script to generate a gnuplot script (or use iteration depending on your set data). Obviously, your image files must be in a format that your version of gnuplot also understands ...
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A possible strategy might be an option plot with rgbimage
in gnuplot.
See the second example here: http://www.gnuplot.info/demo_4.2/image.html
If you are linking a parameter center
to your data points it might be possible.
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