See if you have backed up your files and images then it is easy to get it back on your phone. Otherwise, if the images by mistakenly got deleted then you can also find it with the help of file manager. If you have file manager installed or pre-installed then you can recover them through these steps:
1. Go to file manager
2. Find out the folder where images were saved.
3. Go to thumbnail copy of images in cache.
4. Copy them all and paste somewhere you can get easily.
Size of the file automatically gets small in pixels as it is a thumbnail image.
Best of luck!