AFAIK the photos can only be synced not directly managed.. so if you are getting doubles then you have the image twice in the folder that you have synced..
I had an interesting one last night, i synced my folders of photos then moved the files around and changed the folder to sync, i noticed the memory diagram took away all photos but boosted "other" to 120 megs, much more than it was before, i thought "**** i wont be able to get rid of them now" but on the next sync it all went back to normal and synced the proper files and deleted the other photos.