css里设置

img {
    position: relative;
    z-index: 2;
}

.lazyload-default{
    z-index: 1;
}

<img class="lazy lazyload lazyload-default" src="../../assets/image/img-default.png"/>
<img class="lazy lazyload" :src="item.image_vertical" onl oad="javascript:this.style='display:block';" style="display: none;"/>