Ben,
i am trying to do this now with sales rep images. I have uploaded our images and am curious did you create a segment to call upon or just create a snippet with this naming convention?
We do it all the time!
you need neither segment nor snippet.
※Setting segment and snippet is another way to do this but much more complicated.
Just like Ben said,all you need to do is
1. Upload headshots to your website or Marketo Design Studio.
Make sure the files` name are excitely the same as the Salesforce lead owner`s names.
So the images Url will be like
www.yourwebsite.com/james-bond.jpg
www.yourwebsite.com/sherlock-holmes.jpg
2. Edit the mail, insert images to signature,input Url as below
www.yourwebsite.com/{{lead.Lead Owner First Name}}-{{lead.Lead Owner Last Name}}.jpg
Brilliant! Thank you!