There is a widespread belief that after placing the watermark on the photo you will disable its future using by content thieves. From experience I would say that this is absolutely untrue. Percentage of unique content in the World Wide Web is rapidly decreasing. More and more web projects consist solely of foreign publications. I have seen my photos with my watermark on foreign sites. Some, realizing the inanity of fighting with content "borrowing", generally refuses from the watermarks.
As for me the watermark, nevertheless, is required. Why? Because it saves your authorship, and it is the good advertising of your site. There are 2 main ways how to create a watermark for photos: desktop applications (Image Tuner, Paint, Photoshop, Photo Watermark) and PHP scripts, which can put you previously made watermark at once on all pictures of your website. You can choose that method, which is better exactly in your case. And now i want to tell you some histoical facts about watermark itself.
What is a watermark, each of us knows at least by paper money. This the most common its application eloquently speaks about the appointment of a watermark (which is also called filigree) - to protect money or documents against counterfeitings. However, earlier filigree was used primarily as a brand of the manufacturer of paper, and in the Middle Ages its using was considered mandatory.
Paper factories was called then paper mills, worker - mr. paper master. Master scooped from the vat with a flat netted form powdered and digested in an alkaline solution liquid rag gruel. Each mill has its own Watermark image, which was embroidered on a mesh by a thin wire. When water flows on its embossed surface settle less fibers and paper flat out, repeating the pattern of embroidery. However, the image on the form can be non-convex - be pressed. Then filigree on paper will not be thinner, but, on the contrary, thicker then the rest of the sheet.
Watermark was born in Italy, seven hundred years ago (around 1282). And, as you can see, to use it during manual papermaking process was extremely easy. It was more difficult for it to fit in machine technology. Embroidered bottoms of sieves have replaced lightweight cylinders and rollers with patterned surface - they leave their mark on the still very wet paper web, located on the casted mesh of paper machine. So they come otherwise - moisturize the ready, dry paper and using matrices or patterned rubber roller press the image into it. Such watermarks, unlike the present are correspondingly called artificial, pressed or even rollered.
In one of the museums I happened to meet unique domestic filigree - entire pictures, whose image is hidden at the very sheet of paper. Peaceful landscape, ships which rushes in a stormy sea...
How to see them?
Place electric lamps over the paper sheets. You should turn on the backlight and a smooth surface comes alive: a kind of shadow pictures occur, but very special, with a lot of transitions from light to dark. This drawing is not an engraving, its something else, impressive in its own way: it is hardly believable that such works of applied art were brought to life by not only a creative designs, how much by the desire of artists and specialists of the watermark, who wanted to hone their skills, demonstrate the capabilities of the unusual fine crafts.