How to delete photos given by the smartphone software

I would advice you against deleting such default images or apps if you do not know the exact purpose of the it existence. Some images are part of a larger application. Deleting them may break the app, or even brick your phone.
Are the images you mentioned visible in your Gallery? I guess they would not. If they do, try to find out what app do they belong to. If they are part of some other application, check if you want to remove the app. If the app is part of software, it would not be a good idea to delete them. Check if you want to uninstall the application. Unless the app in question is not part of the software, you can remove it. Doing so will remove the image as well.
For removing system apps, you will need specific apps from Play Store. Search for system app removal tools and install the one that appeals to you.
If you really want to remove the images, get some better file manager. Default file manager does not give access to the system folders. ES File Explorer is one such good example.

The demo files like video, audio and images are designed to give the user an option for user guided tour. Such files should not be deleted using root options. As such deletion could lead to issues when the phone is in demo mode without SIM. Phones like Sony don't allow you to delete with default delete options. And so you should not use the root privilege to delete those images or files.

If you still choose to delete those files at your own risk, then you have to get root access. You can either use root recovery apps or root mode to go through manually and delete the files. Most of the root access apps with UI mode, allows you to delete the files which can't be deleted with normal user access.

The app that can be helpful for you are - ROM Toolbox, Root explorer and SuperSU.