Have you thought about solving this issue in the front end? The client I’m using (Mlem) implemented a feature to directly access the image if the proxy fails. This feature can either be triggered automatically or by pressing a button on the failed image. This allows users the benefit of the proxy while also having the option to give up their IP if they want to see a broken image.
If there was a Lemmy account setting to automatically bypass the proxy on failure then it might not require any front end work, but the manual bypass button would definitely need to be implemented in each client