To create a watermark, you can use a small font like Times New Roman (not too large because we’ll need to be able to see these watermarks across multiple pages), a small size of text, or something simple like this: 
Or this: 
If the watermark you create won’t be readable across multiple pages, you can go from the beginning, and place a ‘–skip’ attribute to stop the watermark from being displayed, though if you use it you will not be able to see what it is for.
Is it really faster to use inline images?
Yes, absolutely! This depends on the image itself – if the image is in an image tag, you can make it to load in a second, because you’re not going to be making this image load up a browser. If you’re going to need to load a lot of images at one time, you can use an HTTP caching library like Nokogiri or something like that. A simple one which you can use from within an HTML page would be something like:
Is it possible to add watermarks that span multiple pages?
Yes, it is very easy! Just make sure to make the images and JavaScript that will be doing it visible to browsers, and then when the page is reloaded, the user should be able to view the watermarks. If you plan to include more than one watermark, you could add them a Javascript like this: 
What are some examples of images that will work
Here are some examples (not all of them are watermarks).
A few are simply HTML text that you can use to illustrate the concepts:
A small picture – so simple, so effective! If you were using them across multiple pages, this might look like:
