Custom image for each contact using merge tag

Custom image for each contact using merge tag

Hi,
I'm wondering if it's possible to set up an email campaign to display a different image for each contact using a custom field for the image url. I tried inserting custom html:

<img src='$[UD:APP_IMAGE_URL||]$'/> but the editor seemed to reject this and did not actually add anything to the email template.

Has anyone got any ideas?

cheers,
Jeremy