I'm not a PhotoShop Guru by any means, but I believe all you need to do is select "Transparent" (instead of White or Background) when creating the logo image. Then when you add it to your picture only the logo should show (not the background of the logo).
In my case, I simply type my copyright and copy it, then paste and place it on each image so that it doesn't interfere with the picture much:
Hope this helps...
Good luck,
ADG Webmaster