help: Add doc for restricting users to change their profile pic.

Fixes part of #14298.

templates/zerver/help/change-your-profile-picture.md

@@ -28,3 +28,7 @@ right corner of the profile picture.  This will remove your current
 profile picture, reverting to the Gravatar default.
 
 {end_tabs}
+
+## Related articles
+
+* [Restrict profile picture changes](/help/restrict-profile-picture-changes)

templates/zerver/help/include/sidebar_index.md

@@ -122,6 +122,7 @@
 * [Restrict private messages](/help/restrict-private-messages)
 * [Restrict user group management](/help/restrict-user-group-management)
 * [Restrict name and email changes](/help/restrict-name-and-email-changes)
+* [Restrict profile picture changes](/help/restrict-profile-picture-changes)
 * [Change who can add custom emoji](/help/only-allow-admins-to-add-emoji)
 * [Block image and link previews](/help/allow-image-link-previews)
 * [Disable message edit history](/help/disable-message-edit-history)

templates/zerver/help/restrict-profile-picture-changes.md

@@ -0,0 +1,21 @@
+# Restrict Profile picture change
+
+{!admin-only.md!}
+
+By default, any user can [change their profile
+picture](/help/change-your-profile-picture).  You can instead prevent
+users from changing their profile picture (primarily useful in
+organizations that are [synchronizing profile pictures from
+LDAP][ldap-sync]) or a similar directory.
+
+[ldap-sync-avatars]: https://zulip.readthedocs.io/en/latest/production/authentication-methods.html#synchronizing-avatars
+
+{start_tabs}
+
+{settings_tab|organization-permissions}
+
+2. Under the **User identity**, select **Prevent users from changing their avatar**.
+
+{!save-changes.md!}
+
+{end_tabs}