First off, Man Up dude and tell your wife to Get A Life outside of worrying about your mental fantasies.
Second, the above posts telling you how to move pics to a different, cleverly titled Folder are all good unless your wife is snoopy enough to simply do a Search for all files ending in ,jpg or other common extensions for photos.
Bottom line is that if she wants badly enough to find your pics, you can't hide them in your home computer.
Suggest you go to Videobox.com, subscribe for I think $14.95 a month
There, you can watch over 2000 porn DVDs. They offer the DVDs scene by scene, so you can then move any scene(s) to MY FAVORITES on the Videobox website (not My Favorites on your own computer).
After a couple months, you'll have a nice file of personal preferences available just by visiting the Videobox site. And she'll never know about it.
BTW, I learned all of the above from SKINSRAJ....Wouldn't know anything about that shit myself....heh