I have an email going out today and am new to Marketo. I have placed an image in by uploading the image to the design section of Marketo and placing it in my campaign. Please note I have cloned an old campaign and edited it according to the new email.
Here's the code for the email and a screenshot of the problem on mobile:
<!-- START OF FULL WIDTH IMAGE-->
<div class="mktEditable" id="geomirror-blog-2" mktoname="geomirror-blog-2">
<p><img src="http://go.didax.com/rs/538-FVP-740/images/Parts120blogImage %28003%29.jpg" alt="Parts120blogImage (003).jpg" height="166" width="600" style="display: block; margin-left: auto; margin-right: auto;" /></p>
<!-- END OF FULL WIDTH IMAGE-->