We have the technology to digitally watermark postage stamps, in order to limit counterfeiting.
What a pity though, that we can still only buy stamps with eg the Queen’s head on them.
Today’s invention is a conventional stamp, complete with the value displayed and a monarch’s head, if necessary. Instead of adding some standard image, chosen by a government representative, why not let people pay to create their own designs for the remaining space? This could easily be done online (by eg uploading their favourite images). The system would then insert covert anti-copying marks into the new stamp which, although invisible, could later be detected by post office sorting machines (after they had been printed out at a specified number of dots per inch by the customer).
Stamps are so century-before-last, but if we must still use them, maybe we could have some fun by designing our own personalised versions?