I had similar problem - I want to replace picture on :hover but can't use BACKGRUND-IMAGE due to lack of Bootstrap's adaptive design.
If you like me only want to change the picture on :hover (but not insist of change SRC for the certain image tag) you can do something like this - it's CSS-only solution.
HTML:
<li>
<img src="/picts/doctors/SmallGray/Zharkova_smallgrey.jpg">
<img class="hoverPhoto" src="/picts/doctors/Small/Zharkova_small.jpg">
</li>
CSS:
li { position: relative; overflow: hidden; }
li img.hoverPhoto {
position: absolute;
top: 0;
right: 0;
left: 0;
bottom: 0;
opacity: 0;
}
li.hover img { /* it's optional - for nicer transition effect */
opacity: 0;
-web-kit-transition: opacity 1s ease;
-moz-transition: opacity 1s ease;li
-o-transition: opacity 1s ease;
transition: opacity 1s ease;
}
li.hover img.hoverPhoto { opacity: 1; }
If you want IE7-compatible code you may hide/show :HOVER image by positioning not by opacity.