I have a theory about those although not totally proven, but one of my household spares was a jock and always trying to take a photo with others which since the last patch they just stand there for ages with nothing happening then it cancels, I noticed those things appearing in my house in spots where she tried to do that and they only started to appear since that patch, since she died I've not found any in my house at all, move objects will enable you to pick them up on a lot you own but otherwise it's as Trip said.
There's quite a few in my town but as long as they aren't blocking routing I've just left them, Rica did say if they became a problem to let her know but so far they haven't, the one outside the bistro door is a little bothersome if there are a few sims about but it doesn't actually block the door so they can get around it.