I am trying to add a screen to a picture so I can use ut as a background on
my web page. Is this possible?
Word knows nothing about screens, which is a technique of breaking the picture
into tiny dots so they can be reproduced by a low-resolution method such as
offset printing.
You can reduce the contrast and increase the brightness of a picture with tools
in Word, giving it a washed-out appearance suitable for a background.
If you really do want to apply a screen, you'll have to do it in a graphics
program that can apply filters.