Can you add an useless parameter?
Something like domain.com/image?dummy=123.
If the server ignores that parameter, you can change the value to a random or incremental number.
I had the same problem with images served by an old app I made long time ago in cherrypy. The right way would have been to use the header to tell the client not to cache the image, but some browsers wouldn’t pay attention to that header. So I added a dummy parameter, which is ignored by the server and prevents the client from caching the image.