I'm concerned that my son has a second iphone, I found a phone charging on the counter yesterday morning and when I pressed the home button, it just said good morning with no lock screen photo. When I asked him about it later, he said it was one of his old ones and pulled it out of a drawer. I pressed the home button and it showed a pic of his dog. I told him that the phone I had seen that morning didn't have a photo, he said he didn't know why and said it must have been because the battery was dead for so long. Is it possible that the lock screen photo could disappear and re-appear on it's own later that day?