Suppose you want the browser to print an image in the place of an h1 with id="title", then the following piece of print CSS does the trick:

#ti\tle { /* 6. */
display: list-item; /* 1. */
list-style-image: url(banner.jpg); /* 2. */
list-style-position: inside; /* 3. */
letter-spacing: -1000em; /* 4. */
font-size: 1pt; /* 5. */
color: #fff; /* 5. */
}