The issue is with caching of Jabber contact photos. Windows and Mac Jabber clients are coded to cache various things. I assume this is an effort to minimize network transactions and optimize client performance. One of the elements cached are contact photos. I have no problem with caching but, in my experience, the issue is that old contact photos tend to be permanently cached and I can't easily (i.e. centrally) force a refresh.
I played around with some options and found a method that worked in some test environments and my own production environment. Maybe this will work for others. I would be interested in hearing about other options. Please use the comments to enlighten me and others!