.imagen-zoom img {
  transition:all 0.5s; 
  -moz-transition:all 0.5s; 
  -webkit-transition:all 0.5s;
  height: 3000px;
}
.imagen-zoom img:hover{
  transform:scale(1.2);
  -moz-transform: scale(1.2);
  -webkit-transform:scale(1.2);
}