The astonishing rapid diffusion of portable devices (i.e. smartphones, tablets, etc.) has had a big, and often positive, impact on our every-day life. These devices have new advanced features developed specifically because of user demand. For example, it is now possible to publish directly the pictures obtained by means of the internal camera of a smartphone on our social network accounts, or on an image hosting service. It is therefore important to have tools, on the portable devices, that can prove the ownership of the pictures and to use them before publishing images. Digital watermarking techniques are commonly used for the copyright protection of images and videos. We have developed a tool for portable devices based on the Android OS that allows the embedding of a digital visible or invisible watermark into a digital image.