Even using the simple watermarking method described, it can be difficult to distinguish some watermarks. Watermarks on stamps printed in yellow and orange can be particularly difficult to see. A few mechanical devices are also used by collectors to detect watermarks on stamps such as the Morley-Bright watermark detector and the more expensive Safe Signoscope. Such devices can be very useful for they can be used without the application of watermark fluid and also allow the collector to look at the watermark for a longer period of time to more easily detect the watermark.
When photos are posted online, they are rarely protected, meaning they can be used by anyone who has access to them. Photos can be protected through copyrights, but a trick often used by photographers is to watermark their photos. Traditionally, watermarks were variations in the thickness of a paper that can only be seen in certain light conditions. Digital watermarks are text or logos that are put on top of the image to establish the owner of the photo. Often, watermarks are opaque and look indented. A great way to ensure that no one is using photos without your permission is to add a watermark with Google's Picasa or Adobe Photoshop. This article will tell you how to add a watermark to photos.