I uploaded pictures and then associated them. In several cases I wanted to later delete the association and yet the picture shown on the family tree remained even though NO picture association was now shown. The only way that I found to get rid of the picture was to delete the person entirely and reinall.
I also found that when using face recognition that it sometimes changed the selected person photo of the person and that this was not changed by a secondary publishing.
Tagging done on the family site now takes priority over changes made in Family Tree Builder with regards to personal photos of people. This solved a long-time problem where people used the online tagging to assign photos to people, and then published again from Family Tree Builder only to lose those assignments to their dismay.
You mentioned that you deleted associations and yet the picture on the family tree remained. This could be a result of caching. Until there is a change in a family tree, it still uses prior information in order to speed up loading time. It's possible that you removed an association and the tree still came up with that association. To clear that, publish a new tree or make a small change in the online tree, and that problem should go away. If it does not, please let me know and include more information about the problem.