The LeadImage behavior provides a mechanism to upload and image as part of an object.
I would like to set the LeadImage from an existing image (already available on the site)
or from some automatic behavior that would use the first image in the text body.
I have had a stab at creating collective.behavior.relatedteaserimage but it is in a "works for me" state. Will create a repo on Github shortly. You can take a look there and see if my approach "works for you"
It's a good start, but I want this image to behave just like a ordinary leadimage (so it shows anywhere a leadimage is expected). An alternative mechanism would be to scan the text body to use the first image as the leadimage. I'll play with the code, thanks.