Were the photos initially stored in the phone's microSD card? If so, you can take the card out, insert it in your computer and run a photo recovery program on it.
Installing and run a Photo Recovery app on your Mac/Win. Choose Photo Recovery from the recovery types.
Click on "Photo" on the main interface. Connect your memory card with Mac, then select the memory device recovery. With "Only scan deleted files" checked, only the lost photo files will be checked.
After hitting on the "Next" button in the previous step, you will get into the photo file scanning section. The app will check files for you intensively. You can have a preview on these photo files during scanning.