Min. Resolution Image: This image will be shown if no other image breakpoint is activated.
Alternative Image 1-3: Each of the alternative images can be activated separately. Additionally you can set up a minimum width for the image to be used on a device. If you use a minimum width of 500px, that image will only be shown on devices with more than 500px of possible width. If you use another image breakpoint at 1000px the first image will be used on devices between 500px and 1000px width. The other one on devices with more than 1000px width.
You can choose the minimum width preselected for iPhone, iPad or custom values up to 5000px