[phillipgessert]

My advice would be to get away from InDesign for this, and also to not set a height value at all. You should also avoid using fixed units like pixels. Instead I would set your landscape photos at width: 100%.

Portrait, I’m less sure. Perhaps start at something like 70% for those, and experiment from there.

<div class="landscape">
<img src="image.jpg" alt="a wide image"/>
</div>

<div class="portrait">
<img src="image2.jpg" alt="a tall image"/>
</div>

.landscape img {
	width: 100%;
}

.portrait img {
	width: 70%;
	margin-left: 15%; 
}