How to easily get rid of the watermark on Windows 8 Consumer Preview
The Windows 8 Consumer Preview places a watermark on the lower-right corner of your wallpaper that reads “Windows 8 Consumer Preview Evaluation copy. Build 8250.” If you want to have a clean desktop, this can be somewhat of an eyesore. You can easily get rid of the watermark without installing any third party software and without having to edit any system files. It should be noted that this method will not work if you are using multiple wallpapers and it will need to be done each time you change your wallpaper, but it is quite simple to do.
1. After you have set the wallpaper that you want for your desktop (remember where it is located, you’ll need it), open Windows Explorer.
2. Go to the Ribbon and click the View tab.
3. In the Show/hide section, check the Hidden items checkbox.

4. Browse to:
\CachedFiles
where your_name is the username for your account. You will see cached image that is your wallpaper.
5. Keep the CachedFiles window open. Open another Windows Explorer window and browse to the location of your wallpaper that you noted in Step 1. Copy the wallpaper image to the CachedFiles window.
6. Right-click the cached wallpaper file, select Rename, and copy the highlighted name, then name the file to something else (I just put a 1 in front of the name).
7. Right-click your wallpaper image, select Rename and paste the copied name as the new name for the file.

8. Go to your desktop. Right-click on an empty space on the screen and select Refresh.
Your wallpaper will now be watermark-free! When you decide to change the wallpaper, just repeat the above steps.