6 images verticales en 380x675px et 3 images horizontales en 1200x675px
<div style=" width:1200px; height:675px; margin:50px 0 50px -20px; border:6px ridge grey; background:white;">
<p id="mgv1" class="mgv"> </p>
<p id="mgv2" class="mgv"> </p>
<p id="mgv3" class="mgv"> </p>
<p id="mgv4" class="mgv"> </p>
<p id="mgv5" class="mgv"> </p>
<p id="mgv6" class="mgv"> </p>
<p id="mgh1" class="mgh"> </p>
<p id="mgh2" class="mgh"> </p>
<p id="mgh3" class="mgh"> </p>
</div>
<style><!--
.mgv{position:absolute; z-index:1; box-sizing:border-box; width:380px; height:200px; margin-top:0px; transition:all 1s;}
#mgv1{background:url('https://i.goopics.net/gvxfek.jpg'); background-size:380px 675px; background-position:0px 0px; transform:translate(0px,0px);}
#mgv2{background:url('https://i.goopics.net/tu6eev.jpg'); background-size:380px 675px; background-position:0px -237px; transform:translate(0px,237px);}
#mgv3{background:url('https://i.goopics.net/ad3ptu.jpg'); background-size:380px 675px; background-position:0px -475px; transform:translate(0px,475px);}
#mgv4{background:url('https://i.goopics.net/x02wnv.jpg'); background-size:380px 675px; background-position:0px 0px; transform:translate(820px,0px);}
#mgv5{background:url('https://i.goopics.net/7qvcfo.jpg'); background-size:380px 675px; background-position:0px -237px; transform:translate(820px,237px);}
#mgv6{background:url('https://i.goopics.net/tu6eev.jpg'); background-size:380px 675px; background-position:0px -475px; transform:translate(820px,475px);}
#mgv1:hover,#mgv2:hover,#mgv3:hover{z-index:5;height:675px; background-position:0px 0px; transform:translate(0px,0px);}
#mgv4:hover,#mgv5:hover,#mgv6:hover{z-index:5;height:675px; background-position:0px 0px; transform:translate(820px,0px);}
.mgh{position:absolute; z-index:1; box-sizing:border-box; width:380px; height:200px; margin-top:0px; transition:all 1s;}
#mgh1{background:url('https://i.goopics.net/446lfr.jpg'); background-size:1200px 675px; background-position:-410px 0px; transform:translate(410px,0px);}
#mgh2{background:url('https://i.goopics.net/hpya5g.jpg'); background-size:1200px 675px; background-position:-410px -237px; transform:translate(410px,237px);}
#mgh3{background:url('https://i.goopics.net/j7vbjy.jpg'); background-size:1200px 675px; background-position:-410px -475px; transform:translate(410px,475px);}
#mgh1:hover,#mgh2:hover,#mgh3:hover{z-index:5;width:1200px;height:675px; background-position:0px 0px; transform:translate(0px,0px);}
--></style>