1. A device for measuring the two-dimensional velocity of a moving paper web having opposed first and second surfaces, wherein comprising: a) at least one light source directed at said first surface and arranged to transmit light through said paper web; b) at least one image capturing device directed at said second surface, and arranged to receive said transmitted light and produce a two-dimensional image of a section of said paper web; c) a control unit, arranged to control said at least one light source and at least one image capturing device, and to receive two-dimensional images from said at least one image capturing device, and comprising computation means arranged to compute the velocity component of said paper web in the machine direction and/or the cross direction by calculating the cross correlation of two two-dimensional images.