I'm having this same issue, have tried most of the solutions in this thread and other threads, none have worked.
I have a 16GB iPhone 5s, using iOS 8.2. I have 9 photos in my photo album, zero videos. On my iPhone, In Settings>General>About, it shows I have 1,239 photos, and 31 videos! Sorry for long message below - just trying to provide all the details in case someone has some insight.
** Also, can anyone clarify what exactly is meant by changing the date suggestion mentioned by txt forever, that worked for several people? Is it referring to backups? This is the one suggestion I haven't tried yet. If it's backups, I may be out of luck. Since my iCloud is always too full and I have to backup to my mac, I only have one backup from about 3 months ago. :/
Details on what I've done so far that HAS NOT WORKED:
So, on my iPhone as mentioned above, In Settings>General>About, it shows I have 1,239 photos, and 31 videos. And in Settings>General>Usage>Storage/Manage Storage it shows Photo and Camera are currently using 2.5 GB. When I view the specifics, it shows only Photo Library which is using the full 2.5GB.
Most recently, today, I backed up my phone to my mac (since iCloud is always too full), Hard Reset my phone (Erased all Data and Content), set my phone back up carefully making sure in iTunes the "Sync Photos (to iPhone) option was off (it has been prior to today anyway). Before and after, iTunes still shows my iPhone's photo storage at 2.53 GB, 1,239 photos.
Recently Deleted was/is also empty and I have no other folders in my Photos (such as Instagram, etc). Even when viewing photos via Collections, Moments view, I still only show the 9 photos, no videos.
In Settings>iCloud>Photos - it has been/is turned off (including every individual option, i.e., iCloud Photo Library (Beta), My Photo Stream, Upload Burst Photos, iCloud Photo Sharing - they are all off). I had already tried various methods of toggling the iCloud settings on and off, meticulously deleting photos from Camera Roll for the last couple months and then immediately deleting them from Recently Deleted, etc. I also frequently delete text threads especially those that include photos.Nothing has worked.
I've been constantly running out of storage ever since I got this iPhone 5s, and that's after decreasing my apps, photos, music by about 70% from what I used to have on previous iPhones including my old iPhone 4s. I constantly and meticulously delete photos, continue to pare down my apps to bare minimum, yet every time a special pic opportunity arises and I open my camera, it says it's too full to take a pic!! Last week for my daughters orchestra concert, I deleted all of my photos, videos and about 10 apps to ensure I had plenty of space. I took 4 videos 1-2 mins each, and no pics, and ran out of space to take anything else before it was even half over. Missed the finale photo opp, etc. I'm definitely ready to make my next smartphone something other than an iPhone at this point. So frustrating!