img {
width: inherit; /* Make images fill their parent's space. Solves IE8. */
max-width: 100%; /* Add !important if needed. */
height: auto; /* Add !important if needed. */
}
또는
img { max-width:100%; height: auto; } /* Enough everywhere except IE8. */
@media \0screen {img { width: auto }} /* Prevent height distortion in IE8. */
정보 출처 : http://stackoverflow.com/questions/8610077/height-auto-in-internet-explorer-8-and-below