This might be too late but I had the same problem...this is what worked for me:
-Settings
-General
-Date & Time
-Removed the "Set Automatically" and then you can manually enter a date.
Set the date for about 3 years ago. eg. Sept 5, 2012
-Then go to Photos
-Albums
-Recently Deleted- Now you will find lots of photos that never were really deleted and are still taking up space on your phone!
-Select
-"Delete All"
-Return to Settings- General- Date & Time and change back to "Set Automatically"
This should delete the photos and free up space.
I even went to the Genius Bar and they couldn't find the photos. I found this solution in a Support Community thread.