Feared of having your images copied online ??  Watermark images online online with web application  PicMarkr . PicMarkr a very useful web application for people who are not good enough on Photoshop or other Windows software . They also have a Windows version of their software available for approximately 40$ s.
Internet version is completely free .So you can watermark unlimited number of images online .

Images can be uploaded from your hard drive(single / batch) or from online photo sharing site Flickr . In the second step , you can choose your watermark text or image and a suitable location for watermark application .

After all ,the picture can be saved or reuploaded  to Flickr on the third step .