EDIT: You haven't rebooted for a month?! Possibly a firewall rule hadn't been applied after the MC25 installation? Original comment below. Your timing was "perfect".
PS: I always reboot my PC twice after Windows Updates these days, as sometimes it just seems to need a second reboot to finish everything.
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There is no option to stop retrieval or display of the image from TMDB.
This will be a firewall issue. Your firewall should allow;
"Program Files\J River\Media Center 25\JRWeb.exe"
"Program Files\J River\Media Center 25\JRWorker.exe"
"Program Files\J River\Media Center 25\Media Center 25.exe"
If you compare the firewall settings for Media Center 25 at home and work you will probably see a difference. If not, look to other firewall settings. Although at work, depending on your work environment, IT people could be blocking all sorts of stuff with complex rules. Like perhaps not allowing image downloads by programs other than a browser, or similar.