What reporting tool are you using? As I know, with RAQ Report, it can be realized with ease. You can make stamp and watermark as background picture. Next, a simple example will tell you how to realize this function easily.
Operation:
Step 1. Make a simple report. As shown below:

Step 2: Set watermark.
Commonly, watermark is set as the background picture of the whole report.
In report IDE, choose "Insert -> Background picture". The dialog box is shown below:

Step 3: Set stamp.
Commonly, stamp is set as the background picture of some specific cells.
Here, we intend to put the stamp at the lower right corner of the report. Right click cell B2, and choose "Data Layer" in the drop-down menu. Then, the dialog box is shown below:

Then, the preview of the report is shown below:

This is only a simple example. If users make a better background picture, the report will be more beautiful.
If you want to know more about RAQ Report, you can refer to
http://www.raqsoft.com/.