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<p>[QUOTE=&quot;Numbers, post: 989475, member: 11668&quot;]I think the fiver from Wikipedia has this one pretty well covered, but just to add some information: The IR-vanishing stripe wasn&#039;t intended as a security feature, per se, but rather as a machine-readability feature.&nbsp; Handheld bill readers, such as those used by the blind, can just look for the IR patterns on the back of the bill to identify the denomination.&nbsp; The two green inks look identical under visible light, so the general public isn&#039;t even aware that the feature exists.&nbsp; By the way, this feature is pretty recent--the earliest printings of the big-head bills don&#039;t have it.&nbsp; It was added around the start of Series 1999, if I remember correctly.&nbsp; (Question for the guy with the camera: Do recent printings of $1&#039;s and $2&#039;s have any IR features on the backs?&nbsp; I&#039;m not sure one way or the other....)</p><p>&nbsp;</p><p>In a similar way, the intaglio portions of the *face* side of the bill are printed with two identical-looking *black* inks, having different magnetic properties.&nbsp; This allows for another form of machine-readability of the notes.&nbsp; The magnetic ink has been around for quite a while longer, all the way back to the later series of small-head notes.[/QUOTE]</p><p><br /></p>

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