From Advanced Photo Tools:
SignMyImage allows you to sign your images. The sign is added directly to the image data. It doesn't use EXIF or stream file properties. The sign stays detectable after jpeg compression, scaling and cropping or for example PrintScreen&Paste*. Now you can pair your signature with your webpage. So when anyone tries to detect the signature in your image, your signature and your webpage will be displayed. It is common to let the application display the detailed information about the author.