If you are not using an Email 2.0 template, then adding Predictive Content in your email can be done simply by tagging an image in your template as a Marketo Editable Image Element.
See docs how to do this:
https://docs.marketo.com/display/DOCS/Email+Template+Syntax#EmailTemplateSyntax-Elements
and code example below:
<div class="mktoImg" id="exampleImg" mktoName="Example Image" mktoImgLink="http://www.marketo.com">
<a><img style="border:10px solid red;"></a>
</div>