there is something that I find kind of strange in the way you phrase things in this post... Your first concern was if it was appropriate for an atheist to believe in ghosts; not if they may be any or not.
This way of thinking is an echo of your past; why should you care what anybody else believes or disbelieves? You treat the label "atheist" as you treated the label "Muslim" in the past. You are iffo, the one and only, that's quite enough for anybody.
Stop worrying what other people think, make up your own mind.
Now let's look at the album and the paint. Before we resort to supernatural explanations, we should try to rule out all obvious,mundane ones. Would you agree that normally the simplest explanation is the most likely.
I often convince myself that I have put my glasses in a certain place, only to later remember, after much seaching, that I was in fact wrong.
You say you are alone in the house, and things get moved around. Well, the obvious question is, who can get and out of your house? Girlfriend? Ex-Girlfriend? Any family members from down the road? Previous lodger?
Try this: Put several smallish bank-notes on the top of the washing machine where the paint did its walk-about. Take a picture of how they look. Leave them for a few days. If they get moved around or vanish, get a locksmith and have the locks changed.