Use a class and CSS rather than an Inline style anyway.
If you want correct aspect ratio and a percentage
<h2><img class="ch-image" src="../Images/ch01.jpg"/><br/>Title</h2>
.h2 {
// no left and right margins (or padding), but do center and set font & size
}
.ch-image {
image-width: 50%;
image-height: auto
}