Why is my available storage reduced when I move a picture from Camera to another named file?

[SteveUWS]

In organizing my pictures, I have created many named files and move new pictures from Camera to those other files. I am using the MOVE function, not the COPY function, but storage space is reduced by the size of the picture file each time I move a picture. What is happening? How do I stop this? Note: When I move a picture back from one of the named files to the Camera file, I recover the storage space. I have a Galaxy S4.