Link it like this:
For example, if the URL is "https://derpibooru.org/images/2486148", the 'id' is 2486148, so, if you type: >>2486148
then it's a link to the image, and looks like this: >>2486148
That way, people can look at it. And if they have it filtered, it will be filtered so they will get a warning or a spoiler if it's something they normally would filter.
Alternatively, you can report the image you tried to report for reason of "other" and in the text field say you want to know why the duplicate was rejected.
Or you can go to the Support channel on Discord (the link is on the Contact page, under the Community column in the footer of the site).
Also, just because people seem to keep missing this fact,
. In all honestly, I think I'm the only staff member who has this thread subscribed any more, and I'm not on staff right now, so I can't even help you.