The main side of a banknote, which bears the most representative motif. Doors and windows feature on the obverse of euro banknotes, symbolising Europe's spirit of openness and co-operation.
A printing method in which an image inked on a planographic surface is printed on an intermediate counter cylinder covered by rubber and from there is transferred to the paper. Dry offset printing, so-called because it does not use water, uses a printing plate with an image. In the case of wet offset printing, the ink of the image is applied to a treated flat plate so that when it is wet with a solution of ink and water, the ink adheres to the parts that form the image, while the water adheres to the parts with no image.
Opacity is defined as a ratio between the light reflected by a single sheet of paper with respect to that reflected by a set of sheets. The ratio value is affected by paper colour. It gives a measure of how more or less transparent a piece of paper is. The appearance and resolution of the features of the watermark will be affected by the opacity of the paper. Opacity is included in the technical specifications for euro banknotes.
Optical character recognition (OCR)
The reading and recognition of characters using an optical device. The numbering on euro banknotes contains optically legible OCR characters.
Optically variable ink
Euro notes use optically variable ink on the reverse of the €50, €100, €200 and €500 denominations. See "Iridescent ink".