Either by providing handlers (overkill?) or setting for different ways the image can work.

From Doug Brethower in 4.3.0alpha1 forum thread:

DB: The image embed with RSS feed is cool and a starting point. I can see a few ways eZ is going with this and very promising. Image click should pull the url datatype rather than just straight link to a bigger image. Code looks already 90 percent there, would be nice to see image click to custom url in RSS feed make it in 4.3 final release version.

AR: Could you describe use case for RSS image url? Can't promise anything for 4.3 though, as we're past feature freeze.

DB: End use is packaging an advertising image with the feed. When user clicks the image, url jumps to advertisers content. Feedburner style. Example is http://feeds.wired.com/wired/ If multiple urls in the content class, pick up the first one.