set style="height:300px !important;" and "imgBanner" for img tag.
<img src="/image/1.jpg" class="imgBanner" style="width:100%; height:300px !important;">
then if you want responsive image, so you can use jquery as:
$.(function(){
$(window).resize(respWhenResize);
respWhenResize();
})
respWhenResize(){
if (pagesize < 578) {
$('.imgBanner').css('height','200px')
} else if (pagesize > 578 ) {
$('.imgBanner').css('height','300px')
}
}