I tried to do so but it didn't change the size:
<div style="height:42px;width:42px">
<img src="http://someimage.jpg">
</div>
What will re-size it (I can't edit/access the img element itself)?
I'm not sure about what you mean by "I have no access to image" But if you have access to parent div you can do the following:
Firs give id or class to your div:
<div class="parent">
<img src="http://someimage.jpg">
</div>
Than add this to your css:
.parent {
width: 42px; /* I took the width from your post and placed it in css */
height: 42px;
}
/* This will style any <img> element in .parent div */
.parent img {
height: 100%;
width: 100%;
}