¿Algo así?
Código CSS:
Ver original.button{
/* Debe tener especificadas las dimensiones
para poder animarlas */
width: 100px;
height: 50px;
background: url(http://placekitten.com/100/100) center center no-repeat;
cursor: pointer;
/* Definir transiciones */
-webkit-transition-property:height, line-height;
-webkit-transition-duration: 0.3s;
-webkit-transition-timing-function: linear;
-moz-transition-property:height, line-height;
-moz-transition-duration: 0.3s;
-moz-transition-timing-function: linear;
transition-property:height, line-height;
transition-duration: 0.3s;
transition-timing-function: linear;
/* Estilos adicionales */
color:#FFF;
font-size: 22px;
font-family: Helvetica, Arial, sans-serif;
line-height: 50px; /* Igual que la altura para centrar verticalmente */
text-align: center;
border-radius: 6px;
box-shadow: 1px 1px 6px rgba(0,0,0,0.5);
border: 1px solid #EEE;
}
.button:hover{
height: 80px;
line-height: 80px;
}