'Correct'
Relative to what
Standard of Measure?
See what I mean?
1) Maintain the (original or a specified) size no matter what .
Stylesheet: width: <use image size in px>; height: <use image size in px>;
2) Stretch to fill the screen, even if it distorts the shape.
Stylesheet: width: 100%; height: 100%;
3) Stretch to fill the screen, But stop the stretching when the shape hit one edge limit
Wrap in a SVG

Calibre created Titlepages will use a SVG wrapper (unless disabled in preferences) if the 'Preserve Cover Aspect Ratio' is ticked in Preferences Output options. (I use this code as my
template in other
controlled image places)