Gmail caches all external urls. That makes it impossible to read the most recent data of the dynamic images (i.e. votes and other server generated images).
- The extension works in background mode and it's logic is executed only if the opened tab URL is https://mail.google.com/*
- In the extension's Option page - you can list all domain names, those you want to enable dynamic images (stop caching).
- Install it directly via Chrome Web Store.
- Or load the extension as unpacked.