The present invention relates to a document to be protected against
forgery, comprising a security feature in the form of a perforation pattern, wherein
the perforation pattern comprises holes with different sizes.
Such a document is disclosed in DE-U-93 15 294.
In this prior art document the perforation pattern takes the form
of a character or a number of characters. The perforation herein is applied in
the form of round perforations with different sizes.
Allthough making these perforations already raises a considerable
barrier for potential forgers, there exists a need for a security feature which
is even more difficult to forge.
This object is achieved by the characterizing features of claim 1.
The perforation pattern is herein formed such that for instance when
the thus treated document is held up against the light or placed on a light box,
an image becomes visible at the location of the perforation pattern.
It will be apparent that arrangement of such an image comprising
brightness tones requires extreme advanced technologies. Such technologies are
not easily accessible to potential forgers, so that documents thus provided with
such a perforation pattern are very difficult to forge.
Another advantage is that at the position of the perforation the
material, for instance paper, plastic or textile is completely removed, so that
when for instance the fingertips brush over the document no elevation or channel
or burr can be felt at all.
If for instance a perforation pattern were to be applied by forgers
by means of for instance conically formed needles, cup-shaped edges or burrs are
always created which are easily discernible with the fingertips. This therefore
provides a good means of identifying possible forgeries.
According to yet another preferred embodiment, the perforation pattern
is a representation of an image arranged on the document by means of a different
Owing to the possibility of visually comparing the image and the
perforation, thus without the deployment of complicated assist means being required,
a less than perfect forgery of just one of the two becomes immediately recognizable.
A high degree of security against fraud is thus obtained.
This measure requires that, in order to make such a document, there
must be present means for making the perforation pattern and means for making the
associated image with a different technique, respectively means for recording
this image and putting it into digital form to enable control of the means necessary
for making a perforation pattern.
According to yet another preferred embodiment, the image arranged
by means of a different technique is specific to the document. This provides the
option of personalizing the document. It will be apparent that this results in
an even higher level of security.
An important application of the present invention lies in the fact
that the document is a passport and that the image is a passport photograph.
Other preferred embodiments are stated in the remaining sub-claims.
It is pointed out here that the invention also relates to a method for applying
a security feature in the form of a perforation pattern in a document, wherein
the perforation pattern is applied by a laser device which is adapted to successively
apply a perforation pattern in the document, wherein the size of the perforation
holes or the density of the perforation holes is controlled by means of an electronic
representation of the image. The present invention will be elucidated hereinbelow
with reference to the annexed figures, in which:
- figure 1 shows a schematic perspective view of a device for manufacturing a
document according to the present invention;
- figure 2 shows a detail view of a perforation pattern such as illustrated in
- figure 3 is a schematic perspective view of a passport according to the present
- figure 4 shows a view of a bank note provided with a pattern according to the
present invention; and
- figure 5 shows a postage stamp provided with a perforation pattern according
to another embodiment of the present invention.
Before discussion of the technique, it is pointed out that in the
present technique the making of brightness tones, as in the graphic art, is possible
by means of perforations which are applied according to fixed grid, wherein the
size of the perforations is a measure for the intensity and that it is also possible
to reproduce brightness tones by making use of perforation holes of equal dimensions,
wherein the density of these dimensions is a measure for the intensity. Both options
can in principle also be combined.
It is pointed out here that in the graphic art the first option is
equivalent to the manner in which black and white photographs are reproduced in
newspapers and that an example of the second technique can be found in the series
of Netherlands postage stamps in which the likeness of Her Majesty the Queen is
represented by dots of varying density.
Shown in figure 1 is a video camera 1 which is directed at a passport
photograph 2. Video camera 1 records the image of passport photograph 2, converts
it into an electronic form and feeds the thus obtained signal to a computer 3
in which it is stored.
The device shown in figure 1 further comprises a laser beam generating
means 4 which is controlled by computer 3. This control relates not only to the
intensity and focussing of the laser beam 5 transmitted by laser device 4, but
also to the direction in which laser beam 5 is transmitted. It is possible to vary
this direction in two planes to apply a perforation pattern 7 in a document 6.
It is pointed out here that such laser devices are known in the prior
art; in order to change the laser light beam use is herein made of mirror systems
not otherwise shown in figure 1.
It is also possible to have laser device 4 stand still and to cause
a carrier on which document 6 is placed to move. It is also possible to cause the
carrier to move in one direction and the laser beam in the other direction; the
choice between the various possibilities depends on the technology used.
Essential is however that perforation pattern 7 comprises perforation
holes of differing diameter, wherein the diameter is a function of the brightness
to be represented in the image. Perforation holes of differing density can be
made by causing the laser beam to generate more or fewer holes locally.
This is illustrated more clearly in figure 2, which shows a detail
of perforation pattern 7. Herein can be seen that in the present embodiment the
perforation pattern is formed by perforation holes 8 which are ordered in a regular
grid, for instance a rectangular grid. The dimension of the holes is herein a measure
for the brightness of the image represented by perforation pattern 7, in the present
case the passport photograph 2. It is noted here that the dimensions of the perforation
holes can be adjusted continuously, thus in principle in analog manner; by processing
with a digital computer a finite, yet large number of stages is however obtained.
Tests have demonstrated that it is nevertheless possible to obtain a representation
of an image which forms an adequate rendering of the relevant image and can be
easily compared therewith.
It will be apparent that in this manner a good authenticity feature
is obtained which is difficult to copy.
Shown in figure 3 is a passport 9 in which the photograph 2 is fixed,
for instance by means of glue, tubular rivets or other manner of attachment. On
the same page, adjacently thereof, a perforation pattern 7 representing the relevant
image is applied. A good comparison can be made by holding up the relevant page
of the passport to the light.
It is otherwise also possible to apply the perforation pattern on
another page of the passport, provided a quick visual comparison is possible. This
makes forgery more difficult since at least two different pages must be forged
for this purpose. It is also possible to apply the image enlarged, reduced in size
or modified in other manner.
Figure 4 shows a banknote 10 which is provided with a perforation
pattern 11, in the present case in the form of an owl. This perforation pattern
is not related to another image arranged on the banknote but forms exclusively
a security feature per se; it is possible to provide banknotes with such a security
feature. It is again pointed out that the different with the prior art lies in
the fact that the image 11 represents different brightness tones, for instance
grey tones. Use is otherwise made herein of a free grid, wherein the dimensions
of the perforations are the same and the density of the perforations varies in
order to represent the grey tones.
The same applies for the postage stamp 12 shown in figure 5 which
is provided with a perforation pattern 13 in the form of a likeness of Her Majesty
the Queen; both forms are herein combined, i.e a varying grid, wherein the dimensions
of the perforations also differ.