Complaints in /var/log/http/error_log: "File does not exist: /[...]/extension/ezflow/design/ezflow/images/th_bg.png"

The file is actually missing...

The cause is: ./packages/ezflow_extension/ezextension/ezflow/design/ezflow/stylesheets/core.css:153:    background-image: url(../images/th_bg.png);