Apparently the name has changed from plone.app.contenttypes.behaviors.leadimage.ILeadImage
to plone.app.contenttypes.behaviors.leadimage.ILeadImageBehavior
The problem in our scenario is that our developer created the addon TTW on Plone 5.2 then moved it to the filesystem.
Then we tested the resulting filesystem addon on Plone 5.1.
Our solution at the moment is to use plone.app.contenttypes.behaviors.leadimage.ILeadImage as this is still supported in Plone 5.2 since the latest plone.app.contenttypes declares it as a formerdottedname