From what I remember, it's Robespierre with fangs in front of a guillotine (or maybe several guillotines), probably some 19th c. British portrayal.
While I'm mithering, if it's Robespierre in front of a lot of guillotines could you be thinking of this anon Thermidorian pamplet? (http://www.google.co.uk/imgres?imgurl=http://media-2.web.britannica.com/eb-media/29/45929-004-37AECE0A.jpg&imgrefurl=http://www.britannica.com/EBchecked/topic-art/505619/38500/Cartoon-engraving-of-Maximilien-de-Robespierre-guillotining-the-executioner-during&usg=__XTZA3j4zMR8r9FMamXTEI10Byjs=&h=450&w=276&sz=31&hl=en&start=7&um=1&itbs=1&tbnid=J0k946bsJ5ma3M:&tbnh=127&tbnw=78&prev=/images%3Fq%3DRobespierre%26um%3D1%26hl%3Den%26client%3Dfirefox-a%26sa%3DN%26rls%3Dorg.mozilla:en-GB:official%26tbs%3Disch:1) No fangs though.
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While I'm mithering, if it's Robespierre in front of a lot of guillotines could you be thinking of this anon Thermidorian pamplet? (http://www.google.co.uk/imgres?imgurl=http://media-2.web.britannica.com/eb-media/29/45929-004-37AECE0A.jpg&imgrefurl=http://www.britannica.com/EBchecked/topic-art/505619/38500/Cartoon-engraving-of-Maximilien-de-Robespierre-guillotining-the-executioner-during&usg=__XTZA3j4zMR8r9FMamXTEI10Byjs=&h=450&w=276&sz=31&hl=en&start=7&um=1&itbs=1&tbnid=J0k946bsJ5ma3M:&tbnh=127&tbnw=78&prev=/images%3Fq%3DRobespierre%26um%3D1%26hl%3Den%26client%3Dfirefox-a%26sa%3DN%26rls%3Dorg.mozilla:en-GB:official%26tbs%3Disch:1) No fangs though.