I have been having similar problems with my jpeg picture files becoming corrupted. When I take the pictures, stored on my SD card, they are fine, but the next day, they are still listed in the gallery, but replaced by generic "black head" place-markers. I searched the internet for information, an applied every solution (short of rooting, because my phone is new and I did not want to void the warranty) Nothing worked. Then, as a precaution, I ordered a brand new Samsung 32gb class 10 SD card. A few days later I went to a wedding and with in 24 hours, at least 1/2 of my pictures stored on my new Samsung SD card were ruined. I then tried to retrieve then directly from the card, and by transferring them to my computer by usb and opening, but they can no longer be read by any programs including my phone.
Interesting fact that I had auto-upload for Dropbox turned on and found the pictures uploaded to Dropbox in various stages of corruption. Some were fine - some were half-picture and half-corrupted - and some were just black head placemarkers that could not be opened. After this, I moved everything back to my phone storage and stopped using the SD card, before the next camera event. (Unfortunately, this max's out my phone) I have no picture problems or corruption with phone-storage, just have no room for pictures or video files.
Yesterday I put the picture evidence from Dropbox and my computer on a flash drive and headed back to the phone store. They told me they could not find anything wrong diagnostically, but said there are a handful of customers that have had problems with SD storage and that it appears to only happen with a 32gb card. They are ordering me a replacement phone and suggested I avoid using a 32gb card in it....use should used either a 16gb or 64gb card as a precaution. So I guess I will be buying ANOTHER sd card and wait to see if this solves the problem.
I have had a considerable amount of frustration with this issue so I decided to post in case anyone else is having a similar problem.