Hi,
in addition to what has already been said:
1. With the help of Joomla's access rights, you can determine which user group is allowed to 'delete' or 'edit'.
You can define the setting for the respective user group once in the JoomGallery options, then this is normally inherited by all categories and images.
Here is a short example: https://www.en.joomgalleryfriends.net/checklist.html
2. In order to prevent a user from changing certain data fields, you have to set a
for the corresponding field in the xml-file.
For the frontend edit form you can find the corresponding file here: ...components/com_joomgallery/models/forms/edit.xml
Then you could leave only the description field changeable for example.
Regards
MrMusic