User can add the images for gallery to display on frontend.
Rather than post types, categories, tags, etc. user will have one more option to add only images for gallery to display.
Gallery Images will contain Gallery Categories. Categories can be multiple for single gallery images.
It will displays like the layout as you have selected.
Below screenshot will display about the adding of gallery images.
Gallery Title: Title of Gallery Images
Gallery Categories: Select more than one categories for gallery images
Gallery Images: Add multiple images for gallery
After the adding the name, images and categories, click on Save Changes.