Código Javascript
:
Ver original/*
<div id="blocker"><img src="img1" alt="img1" width="100" height="100" class="rounded-img" />
<span id="imgHidden"><img src="img2" alt="img2" width="100" height="100" class="rounded-img" /></span>
</div>
<div id="containerTop">
<span id="topBlock" class="bloqueClase">Texto</span>
</div>
*/
<script>
(function(){
document.getElementById("containerTop").onmouseover = function(){
var top = document.getElementById("topBlock"), im = document.getElementById("blocker").firstChild //img1 de blocker
if(im.tagName == 'IMG'){
top.replaceChild(im,top.firstChild) // reemplazar Texto por img1
}
}
})()
</script>