Edit in JSFiddle

#contenedor2{
  max-width: 800px;
  float: left;
  width: 100%;
  overflow: hidden;
  position: relative;
  margin-top: 2px;
}

#cartel21  { 
  background-image: url(http://4.bp.blogspot.com/-i61-SwCZlAg/U_7cELLqkWI/AAAAAAAAGus/tFTcCAZLCEk/s1600/Caja_Amarilla.png);
  height: 233px;
  width: 200px;
  position: relative; 
  float: left;
  left:5%;
  margin-top: -188px;
  
  -webkit-animation:baja 1s;
  -webkit-transition: all 1s;
  -webkit-animation-iteration-count: 4;
  -webkit-animation-direction: alternate;
  
  -moz-animation:baja 1s;
  -moz-transition: all 1s;    
  -moz-animation-iteration-count: 4;
  -moz-animation-direction: alternate;
  
  -o-animation:baja 1s;
  -o-transition: all 1s;    
  -o-animation-iteration-count: 4;
  -o-animation-direction: alternate;
}


#cartel22  { 
  background-image: url(http://1.bp.blogspot.com/-2e6GljTInG0/U_7cEHXhizI/AAAAAAAAGuw/QoZBFX_u91w/s1600/Caja_Morada.png);
  height: 233px;
  width: 200px;
  position: relative; 
  float: left;
  left:10%;
  margin-top: -188px;
 
  -webkit-animation:baja 1s;
  -webkit-transition: all 1s;
  -webkit-animation-iteration-count: 4;
  -webkit-animation-direction: alternate;
  
  -moz-animation:baja 1s;
  -moz-transition: all 1s;    
  -moz-animation-iteration-count: 4;
  -moz-animation-direction: alternate;
  
  -o-animation:baja 1s;
  -o-transition: all 1s;    
  -o-animation-iteration-count: 4;
  -o-animation-direction: alternate;
}

#cartel23  { 
  background-image: url(http://2.bp.blogspot.com/-ZI_xedOlS6M/U_7cEAtIGXI/AAAAAAAAGu0/UY84-niFRig/s1600/Caja_Verde.png);
  height: 233px;
  width: 200px;
  position: relative; 
  float: left;
  left:15%;
  margin-top: -188px;
  
  -webkit-animation:baja 1s;
  -webkit-transition: all 1s;
  -webkit-animation-iteration-count: 4;
  -webkit-animation-direction: alternate;
  
  -moz-animation:baja 1s;
  -moz-transition: all 1s;    
  -moz-animation-iteration-count: 4;
  -moz-animation-direction: alternate;
  
  -o-animation:baja 1s;
  -o-transition: all 1s;    
  -o-animation-iteration-count: 4;
  -o-animation-direction: alternate;
}

#cartel21:hover, #cartel23:hover , #cartel22:hover {
   margin-top:0px; 
  -moz-transition: all 1s; 
  -webkit-transition: all 1s; 
  -o-transition: all 1s; 
}


@-webkit-keyframes baja
{
  0% {margin-top: -188px;}
  100% {margin-top: -180px; }

}

.textos {
  padding-top: 5px;
  background-color: white;
  width: 191px;
  height: 163px;
  margin-top: 5px;
  margin-left: 5px;
  -webkit-border-radius: 10px 10px 10px 10px;
}


#cartel21 p, #cartel22 p, #cartel23 p {
  text-align:center;
  /*font-family: 'Open Sans Condensed', sans-serif;*/
  font-size: 16px;
}

<div id="contenedor2">
   <div id="cartel21"><div class="textos"> <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut est mauris, feugiat ullamcorper enim eu, aliquet tincidunt tortor. Nulla sed malesuada justo, ac semper libero. Nulla magna</p></div> </div>  
</div>