benrobson8 does the same image markup works here on our forums or sandbox ?
If it works here but not on your forum, it might be something to do with a third-party extension.
First you could try to clear the cache via php flarum cache:clear and try again.
If that doesn't fix it, please share with us the output of php flarum info so we can see your setup and which extensions you have enabled.
If your markup doesn't work here either, please show us the image markup here as code (you can put backticks before and after to format as code)
