Responsive design provides appropriate display of your site on mobile phones and tablets.
By default responsive design is enabled. You can disable it in the site settings: Settings → General.
How to prevent images from being cut off on mobile devices
Upload an image first, then add the Title and Text elements. In this case the design will adapt to the screen size and your pages will display correctly on different devices.
Texts incorporated into images are not indexed by web crawlers — your prospective customers won’t be able to find your site.
Moreover, it will be impossible to edit such text later. You will have to change the whole image.