How to set read only permission on all photos for all users

When you set the folder to Read Only, did you get the popup that asked about setting it for the folder only or all the folders and files?

Are the other users admins also?

I just made sure the file was read only, but of course I could delete it because I was the owner.

 

Without knowing how you and others are actually accessing the NAS (browsing to network share or shortcut, mapping a network drive, etc.,) and what format (Fat32 or NTFS) the NAS drive(s) are it is difficult to suggest how you might proceed.
If NTFS you will likely have to edit the NTFS Permissions (Security Tab) in the properties of the folder, individually per user, in the properties of the parent folder by clicking the Advanced button there. And in order to do this successfully you will likely need to break inheritance of that folder from its' parent container by clicking the Change Permissions button and unchecking the box that says Include inheritable permissions from this object's parent (be sure to click the Add button when prompted and not the Remove button or you'll be left with adding back in all your users and groups)
Then you should be able to edit the individual NTFS Security Permissions as you desire (Do not mess with accounts you do not want to manage like SYSTEM or NETWORK, etc., leave them as is).
You can add users or edit existing user permissions from there and for your read only guys you'll want to Allow:
Read Permissions, Traverse folder / execute file, List folder / read data. Make sure you leave one account, presumably yours with full permissions (otherwise you are going to have to go back and take ownership of the folder and start over) and make sure you check the box at the bottom that says Apply these permissions to objects and or containers within the container only. And if you are going to want other to be able to save images to this container they are going to need write permissions, Create Files / Write Data and Create Folders / Append Data.
Perhaps if you are only looking to protect the files and folders from accidental or malicious deletion then an explicit deny check (Delete and Delete subfolders and files) might work better for you, although I have never found it too beneficial to use explicit denies when setting NTFS Permissions.
And you'll want to make sure that no one other than yourself has Change Permissions and Take Ownership to the container.
This is not simple or easy and can result in unintended consequences if not done properly. That's why I normally suggest using a test folder with a single image in it and performing the above action on that folder and determine if the results are as you expect.
Regards
Randy

 

Have you looked into the differences between file security and file sharing?

Also, when you check if it is working, get another user to do that.

 

I don't have a NAS to test, but which one do you have? Does it come with any software to control access or is it like Windows?

 

If the NAS is truly an NTFS volume and it must be because otherwise (fat32) you wouldn't have a security tab in the folder properties. Then setting NTFS permissions should be all you need to do. When share permissions and NTFS security permissions are combined the most restrictive one applies and an explicit deny over rules any and all allows and wins everytime.
You can read this for a more in-depth explanation.
TechExams.Net - MCSA/MCSE 70-290 TechNotes: Shared Folder and NTFS Permissions

 

As Saltgrass has already mention, many such devices come with a Web Interface for configuration.
I would suggest looking more closely at that and perhaps the Device's Forum Boards regarding permissions
DNS-323
Search for permissions