Could any one tell me how to add the unsubscribe link to an image please?
Not sure if Campaignmonitor has this capability but I doubt it. Purely because it is not best practice to have an unsubscribe link on an image. It is bordering on illegal too (if you're a US based company, that is).
The CAN-SPAM law states this regarding unsubscribe links "A visible and operable unsubscribe mechanism is present in all emails."
If you have an email client that doesn't allow images by default then one could argue that until you enable images your unsubscribe link does not meet the criteria.
While Alex is correct that there are draw backs to using an image for your unsubscribe there are times when it works well (for a large call to action in a confirmation email for example), though we still recommend having a plain text unsubscribe link as well.
For those cases you want to just treat the <unsubscribe> tag like an <a href>, since that's what it's converted to. Just put the tags around your image and it'll link it in the final campaign.