Caching in Custom HTML Prompt

I’ve built a macro that downloads an image to a file and then displays it in a custom HTML prompt. When I run this multiple times in a row, the dialog opens with a cached version of the image, right-clicking and choosing ‘reload’ gets the latest one loaded.

For the time being, I’ve added a cache-buster argument to the image path, so it’s working, but I’m wondering if there’s anything that can be done to force the HTML dialog to reload cache. In most circumstances, I really wouldn’t want it to cache at all.

I don’t currently know any other way to stop the caching I’m afraid. I imagine there is some setting somewhere.