First off you must have a image editing program such as Photoshop, Fireworks, Gimp or even MS Paint. Gimp, Is a free program can be found here
http://www.gimp.org/ if you do not already have one. Again this was done in Photoshop but would be close to being the same in most other image programs as well. You will get the hang of it and the knack for it when you begin. Comes a lot easier once you start

We will start with this sample image below as an example.

As you can tell the image has a tag on it already but could easily be remove in an image program by cropping it out since it is in a spot like the bottom that could be removed with out effecting the image really itself.
The way to help this and water mark or copy right your image correctly would be to let say:
Open whatever image you want to water mark in your image program. I am using Photoshop in this tut so just bare with it as the main points would work basically on any image editing program.
You want to try and water mark the image to your best where it covers main parts of the image where it would be real hard to remove. You would want to put lets say for like myspace, you would want to put your URL over the image. By doing this, go ahead and open the image in the program you are using.
in Photoshop you want to select the file tab on top >>> then open >> select the image. Once selected then select the text tool like image below:
click image to zoom in

[ T ] Watermarking your images or designs
Once you select the text tool then select the text and size you want to use to fit image correctly
click image to zoom in

[ T ] Watermarking your images or designs
OK, once thats done then click over top of your image and type your myspace URL or website address URL.
click image to zoom in

[ T ] Watermarking your images or designs
Then you want to select the text layer and grab / hover over the corner of it and drag it across the whole image at an angle like so.
click image to zoom in

[ T ] Watermarking your images or designs
Ok now that the basics are done then you want to add some effects to the text but not to much so that is doesn't take away from the image and also make it a little transparent again so it doesn't take away from the main image that you are water marking so much.
First you want now to select that text layer in the layer palette.
click image to zoom in

[ T ] Watermarking your images or designs
and you want to select a stroke and make it black 2px
click image to zoom in

[ T ] Watermarking your images or designs
OK, now to lighten it up some so it doesn't take away from the main picture, you want to select the blending main options on that same text layer and set the transparency to like 50% like so
click image to zoom in

[ T ] Watermarking your images or designs
And thats all there is to it, you can repeat these steps and put a couple water marks on your image depending how big your image is or certain things you want to make sure is covered and is hard to remove for those type people that like to try and remove them and use as there own. You can also right click on that text layer in the layer palette and select duplicate layer and then just adjust it to where you want it. It basically makes a exact copy of the one you just made.

Well that concludes this one guys, hope it help all you beginners out there and helps protect your pictures or items that you want watermarked. Note: you can also add a copyright symbol to them if needed in the same way. Just go to your rectangle shape tool and right click and select "shape" and up above in your top bar select the shape tool drop down and find the copyright symbol and add it to it as well. Make sure they are copyright before hand before you do so.
Heres the Finished product
Well guys enjoy.
That was just a basic example. Hope it helps.
PS~
NOTE:
Be on the look out for a more detailed version of this and how to add file information into your files that is not editable that is added inside the file format itself as part of its properties. That tut will be coming soon.