[dxld] Graphic signs on waterfall spectrum view

Visiting the SDR online short-wave receiver located at the amateur radio club ETGD at the University of Twente on http://websdr.ewi.utwente.nl:8901/, I have seen at 0140, today Dec 1,  that -centered on 3590 (the 80 meter portion of the receiver, somebody has been transmitting signals that appear as drawings in the waterfall view of the spectrum being showed... Mona Lisa, a butterfly, etc, and a complete phrase ("www.radioscanner.ru"), "travelling" upwards. They look as phantoms :)

How is this done? Haven't seen this before!

Horacio Nigro
Montevideo
Uruguay

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