Abstract: There is provided a security document (10) bearing an image (16) associated with an active substance, wherein the active substance is responsive to tactile pressure (18) in the range 0.01-1O MPa to alter the appearance of the image particularly when viewed under ultraviolet radiation (14). The active substance can be incorporated in an ink forming at least part of the image, in one or more layers associated with or beneath the image, or incorporated within a polymer, or adhesive associated with the image. The active substance comprises at least one of the following: organic or inorganic dye or dyes, chromophore(s), multi-chromophore(s), lumiphore(s). A layer incorporates a UV filter capable of being rendered inoperative in response to pressure, such that tactile pressure thins this layer so that the UV are no longer blocked and reach the lumiphore layer.