I use Photoshop Elements to edit photos for backgrounds
in my powerpoints. I simply go to Image and to Adjust then
to Brightness and Contrast, there I slide the arrows to increase
the brightness to say 80% and drop the contrast to say 25% and
save the image with a BG in front of the name so I'll know it's
for a background (BGmyhouse.jpg). I insert the image as a
background for all pages in the powerpoint so the presentation
will have continuity through out. I don't think it's transparent,
but it's very light and it's under all the other images so you need
not see through it.
Woody in KC