Yes, it is a watermark. Here is how:
- Select the "Page Layout" ribbon at the top of your screen
- Click on "Watermark" and from the drop down menu select "Custom Watermark" at the bottom of the menu
- Click on "Picture", then "Select Picture" from where your picture is lcoated - the "Insert". Adjust the scale of the picture to the size you need for your document and, if necessary, check the "Washout" block (gives a lighter appearance).

Of course, you may have to play around with it to get the appeal you are looking for.

Hope this helps.