Help Dropbox pics But I don't have dropbox!!

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Hello... I purchased a new Gravity recently. When I copied my downloaded pictures and camera pictures to it, (from another android card) and then I went to the gallery, and it had different groups: Download, Camera, a couple of pictures from an audio book folder, My_images, and get this: a folder called "Drop Box" that has two pictures, they're the ones used to sign on to my yahoo account. One I used with a laptop that died, I still have it, but don't use it. Another one a picture I used in a newer laptop to get into yahoo. At first the pictures just showed up as blank icons, and after a couple of days they came across. There is NO Dropbox installed in the phone, nor do I have EVER used dropbox either in the old or new laptop or my old phones. Never accessed yahoo from any of my android phones, so I am puzzled as to why these two pictures are doing there. I'm concerned about deleting them, maybe I can't get into yahoo or something. If anyone knows something about this, please and thank you. Click.